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Here you can find recent articles from Nature, Acta Materialia, Scripta Materialia, Computational Materials Science, Physical Review Letter, Physical Review B, Journal of Physics: Condensed Matter and Science and Engineering A. If you have more suggestions, feel free to write me!

May 19 2020

Irreversible Qubit-Photon Coupling for the Detection of Itinerant Microwave Photons

Raphaël Lescanne, Samuel Deléglise, Emanuele Albertinale, Ulysse Réglade, Thibault Capelle, Edouard Ivanov, Thibaut Jacqmin, Zaki Leghtas, and Emmanuel Flurin

A new single-photon detector minimizes false positives by ensuring that a qubit switches to its excited state if and only if a photon enters a microwave resonator.

Physical Review X

Rectification in Nonequilibrium Parity Violating Metamaterials

Zhenghan Liao, William T. M. Irvine, and Suriyanarayanan Vaikuntanathan

Mathematical analysis of a model network of linked masses on springs reveals how complex patterns of directed energy motion can arise from random fluctuations.

Physical Review X

Tunable Persistent Random Walk in Swimming Droplets

Adrien Izzet, Pepijn G. Moerman, Preston Gross, Jan Groenewold, Andrew D. Hollingsworth, Jérôme Bibette, and Jasna Brujic

The random motion of oil droplets in water is caused by the flow of surfactants at the interface, a finding that gives rise to a broadly tunable swimming system, akin to microorganisms, and allows us to study their self-organization.

Physical Review X

Realization of a Density-Dependent Peierls Phase in a Synthetic, Spin-Orbit Coupled Rydberg System

Vincent Lienhard, Pascal Scholl, Sebastian Weber, Daniel Barredo, Sylvain de Léséleuc, Rukmani Bai, Nicolai Lang, Michael Fleischhauer, Hans Peter Büchler, Thierry Lahaye, and Antoine Browaeys

An array of highly excited “Rydberg atoms” generates an artificial gauge field, a crucial step for creating quantum simulations that rely on strongly interacting topological matter.

Physical Review X

Solvable Models of Supercooled Liquids in Three Dimensions

Tommaso Rizzo and Thomas Voigtmann

We introduce a supercooled liquid model and obtain parameter-free quantitative predictions that are in excellent agreement with numerical simulations, notably in the hard low-temperature region characterized by strong deviations from mode-coupling-theory behavior. The model is the Fredrickson-Anders...

Physical Review Letters

Strumming a Single Chemical Bond

Alfred J. Weymouth, Elisabeth Riegel, Oliver Gretz, and Franz J. Giessibl

Atomic force microscopy and scanning tunneling microscopy can image the internal structure of molecules adsorbed on surfaces. One reliable method is to terminate the tip with a nonreactive adsorbate, often a single CO molecule, and to collect data at a close distance where Pauli repulsion plays a st...

Physical Review Letters

Optical enhancement of dielectric permittivity in reduced lanthanum aluminate

Takayuki Nagai, Akihide Kuwabara, Yu Kumagai, Ichiro Terasaki, and Hiroki Taniguchi

When light is absorbed in solids, electrical conductivity is usually enhanced through generation of photodoped conductive carriers, known as photoconduction. Here we show UV-light absorption restrains photoconduction, but markedly enhances dielectric permittivity in a ceramic sample of $\mathrm{LaAl...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Coherent acoustic phonons generated by ultrashort terahertz pulses in nanofilms of metals and topological insulators

A. Levchuk, B. Wilk, G. Vaudel, F. Labbé, B. Arnaud, K. Balin, J. Szade, P. Ruello, and V. Juvé

We report the generation of coherent acoustic phonons in materials with terahertz ultrashort pulses. This is demonstrated in metals and topological insulators by exciting an acoustic eigenmode in nanometric-sized thin films. The efficiency of the coupling is quadratic in the terahertz electric field...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Pressure-induced decomposition of binary lanthanum intermetallic compounds

Xin Yang, Hefei Li, Hanyu Liu, Hui Wang, Yansun Yao, and Yu Xie

We present a comprehensive study on structural and electronic properties of lanthanum intermetallic compounds (${M}_{x}{\mathrm{La}}_{y}$, $M=\text{Be}$, Mg, Al, Ga, In, Tl, Pb, and Bi) under high pressure. By using a swarm intelligence structure search method combined with first-principles calculat...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Spontaneous ferroelectric order in lead-free relaxor $\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2}\mathrm{Ti}{\mathrm{O}}_{3}$-based composites

Lalitha K. V., Manuel Hinterstein, Kai-Yang Lee, Tiannan Yang, Long-Qing Chen, Pedro B. Groszewicz, Jurij Koruza, and Jürgen Rödel

Short-range ordered polar nanoregions are key to the giant electromechanical properties exhibited by relaxor ferroelectrics. Stabilization of the long-range ferroelectric order in relaxor systems has typically been achieved by applying external fields. In this work, spontaneous (zero-field) ferroele...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

High-pressure structural systematics in samarium up to 222 GPa

S. E. Finnegan, E. J. Pace, C. V. Storm, M. I. McMahon, S. G. MacLeod, H.-P. Liermann, and K. Glazyrin

Angle-dispersive x-ray powder diffraction experiments have been performed on samarium metal up to 222 GPa. Up to 50 GPa we observe the Sm type ($hR9$) $→$ dhcp ($hP4$) $→$ fcc ($cF4$) $→$ distorted fcc ($hR24$) $→\phantom{\rule{4pt}{0ex}}hP3$ transition sequence reported previously. The structure of...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Thermodynamic stabilization of $γ\text{−}\mathrm{U}−\mathrm{Mo}$ alloys: Effect of Mo content and temperature

Aloïs Castellano, François Bottin, Boris Dorado, and Johann Bouchet

The $γ\text{−}\mathrm{U}−\mathrm{Mo}$ alloys have been studied by means of ab initio molecular-dynamic simulations at 900 K as a function of the Mo concentration (0%, 25%, 50%, 75%, and 100%). Using the temperature-dependent effective potential method with the symmetry-imposed force constant extensi...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Extended flat band, entanglement, and topological properties in a Creutz ladder

Yoshihito Kuno

In this work, we study the entanglement and topological properties of an extended flat-band Creutz ladder by considering a compacted localized state (CLS). Based on the CLS picture, we find a multiple flat-band extension from the conventional two flat-band Creutz ladder. A simple vertical interchain...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Structural and thermal transport properties of ferroelectric domain walls in GeTe from first principles

Đorđe Dangić, Éamonn D. Murray, Stephen Fahy, and Ivana Savić

Ferroelectric domain walls are boundaries between regions with different polarization orientations in a ferroelectric material. Using first-principles calculations, we characterize all different types of domain walls forming on ($11\overline{1}$), (111), and ($1\overline{1}0$) crystallographic plane...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

First-principles study of the low-temperature charge density wave phase in the quasi-one-dimensional Weyl chiral compound $({\mathrm{TaSe}}_{4}{)}_{2}\mathrm{I}$

Yang Zhang, Ling-Fang Lin, Adriana Moreo, Shuai Dong, and Elbio Dagotto

Using ab initio density functional theory, we study the lattice phase transition of quasi-one-dimensional $({\mathrm{TaSe}}_{4}{)}_{2}\mathrm{I}$. In the undistorted state, the strongly anisotropic semimetal band structure presents two nonequivalent Weyl points. In previous efforts, two possible Ta-...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Mutual dependence of oxygen and vacancy diffusion in bcc Fe and dilute iron alloys

X. Wang, J. Faßbender, and M. Posselt

A combination of density functional theory (DFT) and an efficient calculation method based on atomistic kinetic Monte Carlo simulations (AKMC) is used to investigate the interdependence of oxygen (O) and vacancy (v) diffusion in bcc Fe and in dilute iron alloys with the substitutional atoms Y and Ti...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Angular dependence of fast-electron scattering from materials

Juri Barthel, Mauricio Cattaneo, Budhika G. Mendis, Scott D. Findlay, and Leslie J. Allen

Angular resolved scanning transmission electron microscopy is an important tool for investigating the properties of materials. However, several recent studies have observed appreciable discrepancies in the angular scattering distribution between experiment and theory. In this paper we discuss a gene...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Optical properties of shock-compressed diamond up to 550 GPa

Kento Katagiri, Norimasa Ozaki, Kohei Miyanishi, Nobuki Kamimura, Yuhei Umeda, Takayoshi Sano, Toshimori Sekine, and Ryosuke Kodama

A series of shock wave experiments were conducted to measure the optical properties of single-crystal diamond $〈100〉$ in the pressure regime between 60 and 550 GPa. The results show that the transparency limit of diamond at 532 nm is $∼170\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. When the applied p...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

High spatial resolution studies of phase transitions within organic aperiodic crystals

Céline Mariette, Laurent Guérin, Philippe Rabiller, Christophe Odin, Mariana Verezhak, Alexei Bosak, Philippe Bourges, Claude Ecolivet, and Bertrand Toudic

The understanding of the symmetry breakings within crystals that are aperiodic by construction is actually very limited. Quasicrystals and incommensurate composite crystals may potentially allow such studies. We focus on the phase transitions of the aperiodic $n$-nonadecane/urea which recovers a tra...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Carbon vacancy-related centers in $3C$-silicon carbide: Negative-$U$ properties and structural transformation

H. J. von Bardeleben, E. Rauls, and U. Gerstmann

Combining electron paramagnetic resonance (EPR) spectroscopy and first-principles density functional theory calculations we have identified the carbon monovacancy center and a second carbon vacancy-related defect, the carbon vacancy–carbon antisite defect in $3C$-SiC. In close analogy to the vacancy...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Origin of the persistence of soft modes in metallic ferroelectrics

Zegnet Yimer and Huaxiang Fu

Metallicity and ferroelectriclike polar distortion are mutually noncompatible, and their coexistence in the same system is an intriguing subject of fundamental interest in the field of structure phase transition. However, it is unclear what mechanism may extend the limit of metallicity that allows p...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Shock compression response of diamond single crystals at multimegabar stresses

J. M. Winey, M. D. Knudson, and Y. M. Gupta

Shock compressed diamond response at multimegabar stresses—of fundamental interest to high pressure science and relevant for high energy density experiments related to inertial confinement fusion—is often assumed to be hydrodynamic. To examine this assumption, plate impact experiments were conducted...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Numerical microstructure model of NiTi wire reconstructed from 3D-XRD data

L Heller, I Karafítov́, L Petrich, Z Pawlas, P Shayanfard, V Beneš, V Schmidt and P Šittner

In this paper, the grain microstructure and strain partitioning in a polycrystalline NiTi wire subjected to tensile loading was reconstructed from an experimental 3D-XRD dataset. The reconstruction of a volume containing more than 8000 stressed grains involved optimization with respect to both the geometrical features and material elastic properties. The geometrical features of the microstructure were reconstructed using Laguerre tessellations based on the experimental 3D-XRD dataset. Two different algorithms fitting Laguerre tessellations were applied in order to assess the sensitivity of the reconstruction to the choice of the algorithm. The material properties in terms of elastic anisotropy were refined from an initial published value to minimize the mismatch between experiment and simulation using an optimization algorithm based on linear elasticity simulations. As a result of this, we constructed a numerical microstructure model that statistically matches the experimentally...

Modelling and Simulation in Materials Science and Engineering

Emergence of directionally-anisotropic mobility in a faceted Ʃ11 ⟨ 110 ⟩ tilt grain boundary in Cu

Megan J McCarthy and Timothy J Rupert

Faceted grain boundaries, where grain boundary area is increased in the name of producing low-energy segments, can exhibit new and unexpected migration trends. For example, several faceted Ʃ3 boundaries have demonstrated anti-thermal and thermally damped mobility. Ʃ11 ⟨110⟩ tilt boundaries represent another promising but relatively unexplored set of interfaces, with a (113) low-energy plane that can lead to faceting. In this study, molecular dynamics simulations are used to study grain boundary migration of an asymmetric Ʃ11 ⟨110⟩ grain boundary in two face centered cubic metals. Mobility of this boundary in Cu is strongly dependent on the direction of the applied driving force. The mobility anisotropy generally becomes smaller, but does not disappear completely, as temperature is increased. In contrast, the same boundary in Al demonstrates similar mobilities in either direction, illustrating that the anisotropic mobility phenomenon is material-dependent. Finally, relationships ...

Modelling and Simulation in Materials Science and Engineering

Quantification of 3D spatial correlations between state variables and distances to the grain boundary network in full-field crystal plasticity spectral method simulations

Markus Kühbach and Franz Roters

Deformation microstructure heterogeneities play a pivotal role during dislocation patterning and interface network restructuring. Thereby, they affect indirectly how the microstructure recrystallizes. Given this relevance, it has become common practice to study the evolution of deformation microstructure heterogeneities with 3D experiments and full-field crystal plasticity computer simulations including tools such as the spectral method. Quantifying material point to grain or phase boundary distances, though, is a practical challenge with spectral method crystal plasticity models because these discretize the material volume rather than mesh explicitly the grain and phase boundary interface network. This limitation calls for specific data post-processing methods to quantify the spatial correlations between state variable values at each material point and the points’ corresponding distance to the closest grain or phase boundary. This work contributes to the development of advanced...

Modelling and Simulation in Materials Science and Engineering

Investigation of partial dislocations fluctuations yields dislocation core parameters

Pierre-Antoine Geslin and David Rodney

In this work, we investigate the thermal fluctuations of dissociated dislocations in face-centered cubic metals. We first derive an analytical expression of the energy of perturbed interacting partial dislocations. Combining this expression with the equipartition theorem yields a prediction for the thermal fluctuations of interacting partials. Comparing this prediction with atomistic calculations in nickel allows to extract the core energy of the partials at finite temperature and as function of their orientation. We also show how to use these values to parameterize the energetics of perfect dislocations and clarify the scope of validity of representing dissociated dislocations as perfect dislocation lines, an approximation customarily made in dislocation dynamics approaches.

Modelling and Simulation in Materials Science and Engineering

An implementation of the phase-field model based on coupled thermomechanical finite element solvers for large-strain twinning, explicit dynamic fracture and the classical Stefan problem

Milovan Zecevic, M J Cawkwell, K J Ramos and D J Luscher

The implementation of a phase-field model in finite elements usually requires significant expertise and involves the development of a user element with additional degrees of freedom. An alternative implementation of the phase-field model within a thermo-mechanical finite element simulation package was presented in (Cho et al 2012 Int. J. Solids Struct. 49 1973–1992), where the phase-field variable is treated as the temperature degree of freedom. However, this approach has only been used for small strain phase-field modelling of martensitic transformations and quasistatic phase-field modelling of fracture. In this work, we present a phase-field finite element implementation via the temperature degree of freedom for several additional cases from the literature: (i) the large-strain phase-field description of deformation twinning presented in (Clayton and Knap 2011 Physica D 240 841–858), (ii) phase-field description of brittle fracture with inert...

Modelling and Simulation in Materials Science and Engineering

May 07 2020

Robust Ferromagnetism in Highly Strained ${\mathrm{SrCoO}}_{3}$ Thin Films

Yujia Wang, Qing He, Wenmei Ming, Mao-Hua Du, Nianpeng Lu, Clodomiro Cafolla, Jun Fujioka, Qinghua Zhang, Ding Zhang, Shengchun Shen, Yingjie Lyu, Alpha T. N’Diaye, Elke Arenholz, Lin Gu, Cewen Nan, Yoshinori Tokura, Satoshi Okamoto, and Pu Yu

A new and unexpected ferromagnetic ground state emerges in highly strained thin films of a transition-metal oxide, shedding new light on electronic and magnetic properties that could be manipulated via strain engineering.

Physical Review X

Origin of Plasticity in Nanostructured Silicon

Zhidan Zeng, Qiaoshi Zeng, Mingyuan Ge, Bin Chen, Hongbo Lou, Xiehang Chen, Jinyuan Yan, Wenge Yang, Ho-kwang Mao, Deren Yang, and Wendy L. Mao

The mechanism of plasticity in nanostructured Si has been intensively studied over the past decade but still remains elusive. Here, we used in situ high-pressure radial x-ray diffraction to simultaneously monitor the deformation and structural evolution of a large number of randomly oriented Si nano...

Physical Review Letters

Unsupervised Manifold Clustering of Topological Phononics

Yang Long, Jie Ren, and Hong Chen

Classification of topological phononics is challenging due to the lack of universal topological invariants and the randomness of structure patterns. Here, we show the unsupervised manifold learning for clustering topological phononics without any a priori knowledge, neither topological invariants no...

Physical Review Letters

Control of strong-field ionization in ferroelectric lithium niobate: Role of the spontaneous polarization

Vincent Wanie, Tian-Jiao Shao, Philippe Lassonde, Heide Ibrahim, Jude Deschamps, Jia-Qi Liu, Fabian Ambriz Vargas, François Vidal, Andreas Ruediger, Francesca Calegari, Xue-Bin Bian, and François Légaré

We report the control of tunnel ionization in lithium niobate (${\mathrm{LiNbO}}_{3}$) using phase-controlled two-color laser fields. Through a macroscopic observable of high contrast, we disclose the crucial contribution of the microscopic spontaneous polarization of the ferroelectric material to t...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Synthetic spin-orbit coupling mediated by a bosonic environment

Mikhail Maslov, Mikhail Lemeshko, and Enderalp Yakaboylu

We study a mobile quantum impurity, possessing internal rotational degrees of freedom, confined to a ring in the presence of a many-particle bosonic bath. By considering the recently introduced rotating polaron problem, we define the Hamiltonian and examine the energy spectrum. The weak-coupling reg...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Optical signatures of phase transitions and structural modulation in elemental tellurium under pressure

Diego Rodriguez, Alexander A. Tsirlin, Tobias Biesner, Teppei Ueno, Takeshi Takahashi, Kaya Kobayashi, Martin Dressel, and Ece Uykur

A room-temperature infrared spectroscopy study of elemental tellurium at pressures up to 8.44 GPa in the energy range $0.015–2$ eV is reported. Optical signatures of the high-pressure polymorphs are investigated and compared to the results of density-functional band-structure calculations. A Drude p...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Possible role of grain-boundary and dislocation structure for the magnetic-flux trapping behavior of niobium: A first-principles study

P. Garg, C. Muhich, L. D. Cooley, T. R. Bieler, and K. N. Solanki

First-principles methods were used to understand magnetic flux trapping at vacancies, dislocations, and grain boundaries in high-purity superconducting niobium. Full-potential linear augmented plane-wave methods were applied in progressively greater complexity, starting at simple vacancies and exten...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

May 06 2020

Optical Nonlocality in Polar Dielectrics

Christopher R. Gubbin and Simone De Liberato

By including nonlocal effects, a new theory provides an accurate description of the optical properties of nanostructures made of polar dielectrics—crystal semiconductors formed from polar molecules.

Physical Review X

Temperature dependence of surface and grain boundary energies from first principles

Daniel Scheiber, Oliver Renk, Maxim Popov, and Lorenz Romaner

In this study we systematically study the temperature dependence of interface energies in W using first principles. To that purpose, we compute interface free energies and consider different contributions, i.e., from lattice expansion, vibrational contribution from harmonic and quasiharmonic approxi...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Enhanced transient negative capacitance during inhomogeneous ferroelectric switching

Bin Xu, Sergey Prosandeev, Charles Paillard, and L. Bellaiche

The reversal of polarization in a ferroelectric material involves overcoming an energy barrier, and has been previously proposed and found to yield transient negative capacitance (NC) in the intermediate states of the switching process. Homogeneous switching was assumed to interpret the experimental...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Theory of finite-temperature two-dimensional structural transformations in group-IV monochalcogenide monolayers

John W. Villanova, Pradeep Kumar, and Salvador Barraza-Lopez

One account of two-dimensional (2D) structural transformations in 2D ferroelectrics predicts an evolution from a structure with ${\mathrm{Pnm}2}_{1}$ symmetry into a structure with square P4/nmm symmetry and is consistent with experimental evidence, while another argues for a transformation into a s...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Computational discovery of a dynamically stable cubic ${\mathrm{SH}}_{3}$-like high-temperature superconductor at 100 GPa via ${\mathrm{CH}}_{4}$ intercalation

Ying Sun, Yifan Tian, Bowen Jiang, Xue Li, Hefei Li, Toshiaki Iitaka, Xin Zhong, and Yu Xie

The 203 K superconductivity of ${\mathrm{SH}}_{3}$ stimulates enormous interest in searching for high-temperature superconductors in compressed hydrides. While several hydrides show high-temperature superconductivity ($>180\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) at extremely high pressure, it is...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Chemical trend of a Cu impurity in Zn chalcogenides

Yang Yang, Peng Zhang, Jingxiu Yang, and Su-Huai Wei

Cu is usually considered as an effective dopant to introduce shallow acceptors in Zn chalcogenides because it is on the left-hand side of Zn in the Periodic Table. Here, using first-principles calculations based on the hybrid functional with spin polarization, we show that contrary to the common exp...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Fourier spectral methods for phase field fracture modelling of CMCs

B Pankowski

Numerical homogenization of multiphase brittle materials, such as ceramic matrix composites is obviously a computationally intensive task. Common approach involving multiscale finite element models remains quite limited to scientific applications instead of being a reasonable alternative for analytical constitutive models. Despite the exponential growth of computational resources (known as Moore’s law) numerical complexity of the underlying algorithms is simply too high to ensure proper scaling to millions of elements. One of the approaches in-between continuous and discrete mechanics is the use of fast Fourier transform (FFT). The aim of this paper is to extend FFT-based methodology beyond its usual elastic regime, using mathematical formalism developed earlier for FE by means of variational principles. Governing equations are formulated in the frequency domain and solved iteratively on a parallel system. Well-known computational specifics of the discrete FFT algorithm itself p...

Modelling and Simulation in Materials Science and Engineering

Theoretical study of post-shock stress relaxation and shock wave deformation around a pore in single and poly-crystalline α-RDX

Yao Long and Jun Chen

The mechanical properties and shock dynamics of α-hexahydro-1,3,5-trinitro-1,3,5-triazine (α-RDX) are simulated by molecular dynamics (MD). Based on the simulation results, the equation of state, Hugoniot curve and isoentropic curve for α-RDX are calculated, and the microscopic structure of shock wave is investigated, including the wave profile and the shock front deformation. First, we prove that the shock wave profile is determined by the viscoelastic equation of α-RDX, and develop a method to inverse the viscoelastic coefficients from the velocity profile calculated by MD. Two stress relaxation mechanisms are obtained: the boundary scattering and molecular rotation. The boundary scattering mechanism shows that the damping time of stress relaxation is determined by the particle size of polycrystal. Second, we find that the pore collapse induces rarefaction wave after the shock front. The rarefaction wave function is evaluated by using the Riemann invariant method, and the shoc...

Modelling and Simulation in Materials Science and Engineering

Impulsive generation of 〈100〉 dislocation loops in BCC iron

A I Bertoni, O R Deluigi, G J Dos Santos, M Perez Díaz and E M Bringa

The conditions for the formation of 〈100〉 dislocation loops in body-centered cubic (BCC) iron were investigated via molecular dynamics simulations using a simplified model intended to mimic conditions in high energy collision cascades, focusing on the possible coherent displacement of atoms at the boundary of a subcascade. We report on the formation of 〈100〉 dislocation loops due to the fast displacement of a few hundred atoms with a coherent acceleration, in agreement with previous results for much larger cascade simulations. We analyze in detail the resulting atomic velocities and pressures, and find that they cannot be described within the usual formalism for a shock regime, since the pressure pulse only lasts less than 1 ps and does not match expected values from a Hugoniot shock. Our simulations include two interatomic potentials: Mendelev, which is extensively used for radiation damage simulations, and Ackland, which has been used for shock simulations because it can repro...

Modelling and Simulation in Materials Science and Engineering

May 01 2020

Observation of Quantized Exciton Energies in Monolayer ${\mathrm{WSe}}_{2}$ under a Strong Magnetic Field

Tianmeng Wang, Zhipeng Li, Zhengguang Lu, Yunmei Li, Shengnan Miao, Zhen Lian, Yuze Meng, Mark Blei, Takashi Taniguchi, Kenji Watanabe, Sefaattin Tongay, Wang Yao, Dmitry Smirnov, Chuanwei Zhang, and Su-Fei Shi

Experiments show for the first time the quantization of exciton energies in a 2D semiconductor exposed to a high magnetic field, setting the stage for explorations of quantized excitons in the presence of strong Coulomb interactions.

Physical Review X

Neural Canonical Transformation with Symplectic Flows

Shuo-Hui Li, Chen-Xiao Dong, Linfeng Zhang, and Lei Wang

A modern machine learning known as normalizing flow can automate cumbersome canonical transformations of Hamiltonian equations, thereby opening up this time-honored technique for studying dynamics to a wide array of complex systems.

Physical Review X

Photonic-Crystal Josephson Traveling-Wave Parametric Amplifier

Luca Planat, Arpit Ranadive, Rémy Dassonneville, Javier Puertas Martínez, Sébastien Léger, Cécile Naud, Olivier Buisson, Wiebke Hasch-Guichard, Denis M. Basko, and Nicolas Roch

A new solution to the phase-matching problem common to so-called traveling-wave parametric amplifiers is achieved with a simple design that’s easy to fabricate.

Physical Review X

Complex Spacing Ratios: A Signature of Dissipative Quantum Chaos

Lucas Sá, Pedro Ribeiro, and Tomaž Prosen

Mathematical tools for distinguishing open quantum systems that are chaotic from those that are exactly solvable fill an important gap in understanding dissipation and decoherence in scenarios relevant to quantum-based technologies.

Physical Review X

Controlled Introduction of Defects to Delafossite Metals by Electron Irradiation

V. Sunko, P. H. McGuinness, C. S. Chang, E. Zhakina, S. Khim, C. E. Dreyer, M. Konczykowski, H. Borrmann, P. J. W. Moll, M. König, D. A. Muller, and A. P. Mackenzie

Experiments reveal that the high conductivity of delafossite oxide materials arises from an extreme degree of purity in their naturally grown crystal structures, a finding that aids the quest for ever-better conductors.

Physical Review X

Spectroscopic and Structural Probing of Excited-State Molecular Dynamics with Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction

Yusong Liu, Spencer L. Horton, Jie Yang, J. Pedro F. Nunes, Xiaozhe Shen, Thomas J. A. Wolf, Ruaridh Forbes, Chuan Cheng, Bryan Moore, Martin Centurion, Kareem Hegazy, Renkai Li, Ming-Fu Lin, Albert Stolow, Paul Hockett, Tamás Rozgonyi, Philipp Marquetand, Xijie Wang, and Thomas Weinacht

The combination of computer simulations and two powerful experimental methods for following molecular change on femtosecond timescales offers an unprecedented view of how a photoexcited molecule breaks apart.

Physical Review X

Thermally Enhanced Electro-osmosis to Control Foam Stability

Oriane Bonhomme, Li Peng, and Anne-Laure Biance

Electric fields can control the stability of liquid foams, a versatile material used in many industrial applications that is otherwise difficult to stabilize or destabilize on demand.

Physical Review X

Light-Driven Raman Coherence as a Nonthermal Route to Ultrafast Topology Switching in a Dirac Semimetal

C. Vaswani, L.-L. Wang, D. H. Mudiyanselage, Q. Li, P. M. Lozano, G. D. Gu, D. Cheng, B. Song, L. Luo, R. H. J. Kim, C. Huang, Z. Liu, M. Mootz, I. E. Perakis, Y. Yao, K. M. Ho, and J. Wang

A light-induced phase transition in a Dirac material offers insight into how these materials respond to periodic driving (that is, quantum back-and-forth motion), information necessary for topology-based quantum computation and topological transistors.

Physical Review X

Quantum Logic Spectroscopy with Ions in Thermal Motion

D. Kienzler, Y. Wan, S. D. Erickson, J. J. Wu, A. C. Wilson, D. J. Wineland, and D. Leibfried

An enhanced version of quantum logic spectroscopy, used to map absorption and emission from single atoms, tolerates some ion motion and entangles several ions for improved sensitivity.

Physical Review X

Interacting Polaron-Polaritons

Li Bing Tan, Ovidiu Cotlet, Andrea Bergschneider, Richard Schmidt, Patrick Back, Yuya Shimazaki, Martin Kroner, and Ataç İmamoğlu

Photons in certain materials can form massive, strongly interacting quasiparticles, giving rise to nonlinear effects that could be useful in quantum optics.

Physical Review X

Field-Angle-Resolved Magnetic Excitations as a Probe of Hidden-Order Symmetry in ${\mathrm{CeB}}_{6}$

P. Y. Portnichenko, A. Akbari, S. E. Nikitin, A. S. Cameron, A. V. Dukhnenko, V. B. Filipov, N. Yu. Shitsevalova, P. Čermák, I. Radelytskyi, A. Schneidewind, J. Ollivier, A. Podlesnyak, Z. Huesges, J. Xu, A. Ivanov, Y. Sidis, S. Petit, J.-M. Mignot, P. Thalmeier, and D. S. Inosov

A novel approach to analyzing neutron-scattering data offers a new way to probe magnetic order arising from higher-order electron multipoles.

Physical Review X

Learning Force Fields from Stochastic Trajectories

Anna Frishman and Pierre Ronceray

Reconstructing a stochastic dynamical model from single noisy trajectories of complex Brownian systems is made possible by an efficient force inference technique.

Physical Review X

Repetitive Quantum Nondemolition Measurement and Soft Decoding of a Silicon Spin Qubit

Xiao Xue, Benjamin D’Anjou, Thomas F. Watson, Daniel R. Ward, Donald E. Savage, Max G. Lagally, Mark Friesen, Susan N. Coppersmith, Mark A. Eriksson, William A. Coish, and Lieven M. K. Vandersypen

An experiment measures an individual electron spin with high fidelity and without demolishing it, thus setting the stage for robust quantum error correction with spin qubits in silicon.

Physical Review X

3D Spatial Exploration by E. coli Echoes Motor Temporal Variability

Nuris Figueroa-Morales, Rodrigo Soto, Gaspard Junot, Thierry Darnige, Carine Douarche, Vincent A. Martinez, Anke Lindner, and Éric Clément

Experiments show that bacteria constantly alter their exploration states—frequent directional changes and persistent swimming—which could provide insight into the onset of infections and the dynamics of microbial communities.

Physical Review X

Absence of a Dissipative Quantum Phase Transition in Josephson Junctions

A. Murani, N. Bourlet, H. le Sueur, F. Portier, C. Altimiras, D. Esteve, H. Grabert, J. Stockburger, J. Ankerhold, and P. Joyez

Experiments show that, contrary to long-held predictions, a Josephson junction in series with a large enough resistance does not become insulating at low temperature, thus forcing a reanalysis of quantum phase transitions in these and similar systems.

Physical Review X

Equation of State of Liquid Iron under Extreme Conditions

Yasuhiro Kuwayama, Guillaume Morard, Yoichi Nakajima, Kei Hirose, Alfred Q. R. Baron, Saori I. Kawaguchi, Taku Tsuchiya, Daisuke Ishikawa, Naohisa Hirao, and Yasuo Ohishi

The density of liquid iron is measured experimentally at conditions that match those inside Earth.

Physical Review Letters

Fully Coupled Two-Fluid Dynamics in Superfluid $^{4}\mathrm{He}$: Anomalous Anisotropic Velocity Fluctuations in Counterflow

Satoshi Yui, Hiromichi Kobayashi, Makoto Tsubota, and Wei Guo

We investigate the thermal counterflow of the superfluid $^{4}\mathrm{He}$ by numerically simulating three-dimensional fully coupled dynamics of the two fluids, namely quantized vortices and a normal fluid. We analyze the velocity fluctuations of the laminar normal fluid arising from the mutual fric...

Physical Review Letters

Many-Body Dynamical Localization in a Kicked Lieb-Liniger Gas

Colin Rylands, Efim B. Rozenbaum, Victor Galitski, and Robert Konik

The kicked rotor system is a textbook example of how classical and quantum dynamics can drastically differ. The energy of a classical particle confined to a ring and kicked periodically will increase linearly in time whereas in the quantum version the energy saturates after a finite number of kicks....

Physical Review Letters

Lognormal Distribution of Local Strain: A Universal Law of Plastic Deformation in Material

Ao Tang, Haiting Liu, Guisen Liu, Yong Zhong, Li Wang, Qi Lu, Jeff Wang, and Yao Shen

Given the infinite diversity of microstructural inhomogeneity, the variation in spatial distribution of local strain could be infinite. However, this study finds that the statistical distribution of local strain universally follows a lognormal distribution irrespective of phase content and deformati...

Physical Review Letters

Structural Ordering in Liquid Gallium under Extreme Conditions

James W. E. Drewitt, Francesco Turci, Benedict J. Heinen, Simon G. Macleod, Fei Qin, Annette K. Kleppe, and Oliver T. Lord

The atomic-scale structure, melting curve, and equation of state of liquid gallium has been measured to high pressure ($p$) and high temperature ($T$) up to 26 GPa and 900 K by in situ synchrotron x-ray diffraction. Ab initio molecular dynamics simulations up to 33.4 GPa and 1000 K are in excellent ...

Physical Review Letters

Anharmonic Eigenvectors and Acoustic Phonon Disappearance in Quantum Paraelectric ${\mathrm{SrTiO}}_{3}$

Xing He, Dipanshu Bansal, Barry Winn, Songxue Chi, Lynn Boatner, and Olivier Delaire

Pronounced anomalies in the ${\mathrm{SrTiO}}_{3}$ dynamical structure factor, $S(\mathbf{Q},E)$, including the disappearance of acoustic phonon branches at low temperatures, were uncovered with inelastic neutron scattering (INS) and simulations. The striking effect reflects anharmonic couplings bet...

Physical Review Letters

Performance of the standard exchange-correlation functionals in predicting melting properties fully from first principles: Application to Al and magnetic Ni

Li-Fang Zhu, Fritz Körmann, Andrei V. Ruban, Jörg Neugebauer, and Blazej Grabowski

We apply the efficient two-optimized references thermodynamic integration using Langevin dynamics method [Phys. Rev. B 96, 224202 (2017)] to calculate highly accurate melting properties of Al and magnetic Ni from first principles. For Ni we carefully investigate the impact of magnetism on the liquid...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Local vibrational modes of Si vacancy spin qubits in SiC

Z. Shang, A. Hashemi, Y. Berencén, H.-P. Komsa, P. Erhart, S. Zhou, M. Helm, A. V. Krasheninnikov, and G. V. Astakhov

Silicon carbide is a very promising platform for quantum applications because of the extraordinary spin and optical properties of point defects in this technologically friendly material. These properties are strongly influenced by crystal vibrations, but the exact relationship between them and the b...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Prediction of a novel high-pressure phase of hydrogen peroxide

Xinyu Zhang, Wenbo Zhao, Siyu Liu, Lihua Yang, Qing Guo, Jian Lv, and Yanchao Wang

The binary H-O system almost exclusively exists in the form of water ice with stoichiometry of ${\mathrm{H}}_{2}\mathrm{O}$ in a wide range of pressure (∼5 TPa) that is one of the most abundant substances in the solar system. Hydrogen peroxide (${\mathrm{H}}_{2}{\mathrm{O}}_{2}$) is only metastable ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

${\mathrm{Bi}}_{2}{\mathrm{W}}_{2}{\mathrm{O}}_{9}$: A potentially antiferroelectric Aurivillius phase

Hania Djani, Emma E. McCabe, W. Zhang, P. S. Halasyamani, A. Feteira, Jordan Bieder, Eric Bousquet, and Philippe Ghosez

Ferroelectric tungsten-based Aurivillius oxides are naturally stable superlattice structures, in which $A$-site deficient perovskite blocks ${[{\mathrm{W}}_{n}{\mathrm{O}}_{3n+1}]}^{−2}$ ($n=1,2,3,⋯$) interleave with fluorite-like bismuth oxide layers ${[{\mathrm{Bi}}_{2}{\mathrm{O}}_{2}]}^{+2}$ alo...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Experimental characterization of spin-$\frac{3}{2}$ silicon vacancy centers in $6H$-SiC

Harpreet Singh, Andrei N. Anisimov, Sergei S. Nagalyuk, Eugenii N. Mokhov, Pavel G. Baranov, and Dieter Suter

Silicon carbide (SiC) hosts many interesting defects that can potentially serve as qubits for a range of advanced quantum technologies. Some of them have very interesting properties, making them potentially useful, e.g., as interfaces between stationary and flying qubits. Here we present a detailed ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Gauging defects in quantum spin systems: A case study

Jacob C. Bridgeman, Alexander Hahn, Tobias J. Osborne, and Ramona Wolf

The goal of this work is to build a dynamical theory of defects for quantum spin systems. This is done by explicitly giving an exhaustive case study of a one-dimensional spin chain with $\mathbf{Vec}(\mathbb{Z}/2\mathbb{Z})$ fusion rules, which can easily be extended to more general settings. A kine...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Atomic-scale origin of ultrahigh piezoelectricity in samarium-doped PMN-PT ceramics

Chunchun Li, Bin Xu, Dabin Lin, Shujun Zhang, Laurent Bellaiche, Thomas R. Shrout, and Fei Li

Designing high-performance piezoelectric materials based on atomic-scale calculations is highly desired in recent years, following the understanding of the structure-property relationship of state-of-the-art piezoelectric materials. Previous mesoscale simulations showed that local structural heterog...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Structural and electronic properties of two-dimensional freestanding $\mathrm{BaTi}{\mathrm{O}}_{3}/\mathrm{SrTi}{\mathrm{O}}_{3}$ heterostructures

Fanhao Jia, Shaowen Xu, Guodong Zhao, Chao Liu, and Wei Ren

The successful preparation of the freestanding perovskite materials down to the monolayer limit [Ji et al., Nature (London) 570, 87 (2019)] provided the opportunity to make the two-dimensional (2D) oxide and heterostructure, which could be significantly distinctive from the conventional oxide super...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Shocked ceramics melt: An atomistic analysis of thermodynamic behavior of boron carbide

Matthew DeVries, Ghatu Subhash, and Amnaya Awasthi

Macroscale experiments for structural response of materials often do not capture deformation features at the atomistic scale. This limitation becomes more pronounced in materials subjected to shock loading, especially in covalently bonded ceramics such as boron carbide, which exhibit a deleterious m...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Comment on “Thermal vacancies in random alloys in the single-site mean-field approximation”

Dane Morgan and Yongfeng Zhang

This comment concerns the contribution of configurational mixing entropy to the change in the total Gibbs free energy in the process of vacancy formation and the consequent effect on the thermal equilibrium vacancy concentration in multicomponent alloys. A different derivation is shown than that in ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Nucleation mechanism for $\mathrm{hcp}→\mathrm{bcc}$ phase transformation in shock-compressed Zr

Hongxiang Zong, Ping He, Xiangdong Ding, and Graeme J. Ackland

We present large-scale atomic simulations of shock-induced phase transition in Zr assisted by the machine learning method. The results indicate that there exists a critical piston velocity of ${U}_{\mathrm{p}}∼0.85\phantom{\rule{0.16em}{0ex}}\mathrm{km}/\mathrm{s}$, above which the product phase has...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Thickness dependence of hydrogen-induced phase transition in ${\mathrm{MoTe}}_{2}$

Priyanka Manchanda, Pankaj Kumar, and Pratibha Dev

Two-dimensional (2D) transition metal dichalcogenides (TMDs) usually exist in two or more structural phases with different physical properties, and can be repeatedly switched between these phases via different stimuli, making them potentially useful for memory devices. An understanding of the physic...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Observation of a 1.979-eV spectral line of a germanium-related color center in microdiamonds and nanodiamonds

V. S. Krivobok, E. A. Ekimov, S. G. Lyapin, S. N. Nikolaev, Yu. A. Skakov, A. A. Razgulov, and M. V. Kondrin

Color centers in diamond are considered as a platform for quantum computing and communications, biomedical markers, and nanosensors. Negatively charged split-vacancy centers have outstanding properties due to bright and almost monochromatic luminescence, but they have poor spin coherence and relaxat...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

High-temperature superconductivity in the Ti-H system at high pressures

Jin Zhang, Jeffrey M. McMahon, Artem R. Oganov, Xinfeng Li, Xiao Dong, Huafeng Dong, and Shengnan Wang

Search for stable high-pressure compounds in the Ti-H system reveals the existence of titanium hydrides with new stoichiometries, including $Ibam\text{−}{\mathrm{Ti}}_{2}{\mathrm{H}}_{5}$, $I4/m\text{−}{\mathrm{Ti}}_{5}{\mathrm{H}}_{13}$, $I\overline{4}\text{−}{\mathrm{Ti}}_{5}{\mathrm{H}}_{14}$, $F...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Prediction of $\mathrm{F}{\mathrm{e}}_{2}\mathrm{P}$-type $\mathrm{TiT}{\mathrm{e}}_{2}$ under pressure

Kai Hu, Jichun Lian, Li Zhu, Qinjun Chen, and Sheng-Yi Xie

$\mathrm{F}{\mathrm{e}}_{2}\mathrm{P}$-type dioxides are significant both for geoscience and condensed-matter physics. For example, $\mathrm{F}{\mathrm{e}}_{2}\mathrm{P}$-type $\mathrm{Si}{\mathrm{O}}_{2}$ has been proposed to be one of the dominant components in the mantles of super-Earths and $\ma...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Temperature-induced structural change through the glass transition of silicate glass by neutron diffraction

Ying Shi, Ozgur Gulbiten, Jörg Neuefeind, Dong Ma, Albert P. Song, Bryan Wheaton, Mathieu Bauchy, and Stephen R. Elliott

Supercooled silicate liquids exhibit several orders of magnitude increase in viscosity at the glass-transition temperature (${T}_{\mathrm{g}}$) towards the glassy state. Such a drastic dynamical slowdown leads to an abrupt change in the slope of temperature-dependent thermodynamic properties because...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Elastic Hamiltonians for quantum analog applications

Choonlae Cho, Sunkyu Yu, and Namkyoo Park

Elastic waves are complex mixtures of transverse and longitudinal oscillations even in isotropic and homogeneous media, in contrast to the quantum, electromagnetic, or acoustic waves which could share the same formalism of Hamiltonian and application techniques. Here, we reformulate the elastic wave...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Breakdown of Arrhenius law of temperature-dependent vacancy concentration in fcc lanthanum

Lucian Mathes, Thomas Gigl, Michael Leitner, and Christoph Hugenschmidt

We measured the temperature-dependent equilibrium vacancy concentration using in situ positron annihilation spectroscopy in order to determine the enthalpy ${H}_{\text{f}}$ and entropy ${S}_{\text{f}}$ of vacancy formation in elementary fcc La. The Arrhenius law applied for the data analysis, howeve...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Iodine interstitials as a cause of nonradiative recombination in hybrid perovskites

Xie Zhang, Mark E. Turiansky, Jimmy-Xuan Shen, and Chris G. Van de Walle

The identification of deep-level defects that act as detrimental nonradiative recombination centers is critical for optimizing the optoelectronic performance of hybrid perovskites. Although extensive studies have been devoted to revealing the nature of deep-level defects in hybrid perovskites, it is...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Persistent insulating state at megabar pressures in strongly spin-orbit coupled $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$

Chunhua Chen, Yonghui Zhou, Xuliang Chen, Tao Han, Chao An, Ying Zhou, Yifang Yuan, Bowen Zhang, Shuyang Wang, Ranran Zhang, Lili Zhang, Changjin Zhang, Zhaorong Yang, Lance E. DeLong, and Gang Cao

It is commonly anticipated that an insulating state will collapse in favor of an emergent metallic state at high pressures: The average electron density must increase with pressure, while the electronic bandwidth is expected to broaden and fill the insulating energy band gap. Here we report an unusu...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Role of spin-orbit coupling in the alloying behavior of multilayer ${\mathrm{Bi}}_{1−x}{\mathrm{Sb}}_{x}$ solid solutions revealed by a first-principles cluster expansion

A. Ektarawong, T. Bovornratanaraks, and B. Alling

We employ a first-principles cluster-expansion method in combination with canonical Monte Carlo simulations to study the effect of spin-orbit coupling on the alloying behavior of multilayer ${\mathrm{Bi}}_{1−x}{\mathrm{Sb}}_{x}$. Our simulations reveal that spin-orbit coupling plays an essential rol...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Quantum and thermal fluctuations of a thin elastic plate

Dennis P. Clougherty and Eliot Heinrich

We consider a Hamiltonian description of the vibrations of a clamped, elastic circular plate. The Hamiltonian of this system features a potential energy with two distinct contributions: one that depends on the local mean curvature of the plate and a second that depends on its Gaussian curvature. We ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Symmetry breakings in a metal organic framework with a confined guest

Céline Mariette, Elżbieta Trzop, Jean-Yves Mevellec, Abdou Boucekkine, Aziz Ghoufi, Guillaume Maurin, Eric Collet, M. Carmen Muñoz, José Antonio Real, and Bertrand Toudic

The MOF $[{\text{Fe(tvp)}}_{2}{(\text{NCS})}_{2}]·2\text{BzCHO}$ is demonstrated to undergo a complex sequence of phase transitions and spin-crossover behavior of its constitutive ${\text{Fe}}^{\text{II}}$ ions upon adsorption of benzaldehyde guest molecules. Our study, combining Raman and synchrotr...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Single-layer Janus black arsenic-phosphorus (b-AsP): Optical dichroism, anisotropic vibrational, thermal, and elastic properties

L. L. Li, C. Bacaksiz, M. Nakhaee, R. Pentcheva, F. M. Peeters, and M. Yagmurcukardes

By using density functional theory (DFT) calculations, we predict a puckered, dynamically stable Janus single-layer black arsenic-phosphorus (b-AsP), which is composed of two different atomic sublayers, arsenic and phosphorus atoms. The calculated phonon spectrum reveals that Janus single-layer b-As...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Prediction of perovskite-related structures in $A{\mathrm{CuO}}_{3−x}$ ($A$ = Ca, Sr, Ba, Sc, Y, La) using density functional theory and Bayesian optimization

Atsuto Seko and Shintaro Ishiwata

Here, the authors predict the stability of oxygen-deficient perovskite structures in cuprates by density functional theory calculations. They introduce a combination of cluster expansion, Gaussian process, and Bayesian optimization to find stable oxygen-deficient structures. The calculations not only reproduce the reported structures but suggest the presence of unknown oxygen-deficient perovskite structures, some of which are stabilized at high pressures. This work demonstrates the great applicability of the present computational procedure for the elucidation of the structural stability of strongly correlated oxides.

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Atomistic simulations of dynamics of an edge dislocation and its interaction with a void in copper: a comparative study

Wu-Rong Jian, Min Zhang, Shuozhi Xu and Irene J. Beyerlein

Atomistic simulation methods are appropriate tools for investigating the dynamics of dislocations and their interactions with obstacles in metallic materials. In particular, molecular dynamics (MD) simulations have been widely employed on these two topics in the past several decades. However, even for the same type of simulation, the results can vary. While some of the quantitative differences may be due to the choices of interatomic potential and simulation cell size, they could similarly be attributed to choice of model settings, which have also differed substantially to date. In this paper, we carry out systematic MD simulations to study the effects of a few key model settings on the dynamics of an edge dislocation and its interaction with a void in copper. For a fixed interatomic potential, three modeling parameters, including applied loading mode, boundary conditions, and thermostat, are considered and their influences on the stress–strain response, the dislocation velocity...

Modelling and Simulation in Materials Science and Engineering

Improved energy minimization of iron–carbon systems: on the influence of positioning interstitial atoms

Nina Gunkelmann and Maximilian Merkert

We compare different optimization schemes for the energy minimization in iron–carbon single crystals, where either choosing an initial distribution of interstitial atoms is followed by a conjugate gradient algorithm, or a simulated annealing (SA) procedure is employed. As an alternative to random or so-called single-atom starting configurations, globally optimal interstitial sites with respect to a long-range potential for the carbon–carbon interaction are computed by exact methods of discrete optimization. A comparison of the mechanical properties of the corresponding systems reveals that the positioning scheme can have a large influence. The elastic properties of the crystals for initially randomly distributed carbon atoms show large fluctuations for different initial C interstitial positions. The solution by SA is superior but still causes significant deviations, while using the optimized configurations leads to an increased stiffness of the Fe–C system.

Modelling and Simulation in Materials Science and Engineering

April 02 2020

Implementing Optogenetic Modulation in Mechanotransduction

Miao Yu, Shimin Le, Samuel Barnett, Zhenhuan Guo, Xueying Zhong, Pakorn Kanchanawong, and Jie Yan

Experiments show that light-induced dimerization can be used to control the connectivity of force-transmission linkages in cells, providing a new way to study how cells react to mechanical stimuli.

Physical Review X

Magnetic-Field-Induced Quantum Phase Transitions in a van der Waals Magnet

Siwen Li, Zhipeng Ye, Xiangpeng Luo, Gaihua Ye, Hyun Ho Kim, Bowen Yang, Shangjie Tian, Chenghe Li, Hechang Lei, Adam W. Tsen, Kai Sun, Rui He, and Liuyan Zhao

Spectroscopic measurements explain why a van der Waals ferromagnet displays different magnetic behavior in its layered and bulk forms.

Physical Review X

Complex Distributions Emerging in Filtering and Compression

G. J. Baxter, R. A. da Costa, S. N. Dorogovtsev, and J. F. F. Mendes

A simple filter for marking patterns in a binary sequence produces an output with similar statistics to cooperative systems such as spin glasses and neural networks, providing a potential tool for understanding the statistics in those systems as well.

Physical Review X

Deep Quantum Geometry of Matrices

Xizhi Han (韩希之) and Sean A. Hartnoll

Neural networks enable an important calculation in a popular approach to unifying quantum theory with general relativity.

Physical Review X

Characterizing Multiphoton Excitation Using Time-Resolved X-ray Scattering

Philip H. Bucksbaum, Matthew R. Ware, Adi Natan, James P. Cryan, and James M. Glownia

Using femtosecond x-ray scattering, experiments reveal the ultrafast and ultrasmall motion of molecular iodine in response to intense laser radiation, showing that femtosecond x rays are a powerful tool for studying laser-matter interactions.

Physical Review X

Observation of Anomalous Non-Ohmic Transport in Current-Driven Nanostructures

Guanxiong Chen, Ryan Freeman, Andrei Zholud, and Sergei Urazhdin

Microstructure response to electrical current cannot be described as Joule heating, which warrants a reexamination of many observations of current-induced heating and suggests a new way to study the electron-phonon interaction.

Physical Review X

Microscopic Origin of Capillary Force Balance at Contact Line

JingCun Fan, Joël De Coninck, HengAn Wu, and FengChao Wang

We investigate the underlying mechanism of capillary force balance at the contact line. In particular, we offer a novel approach to describe and quantify the capillary force on the liquid in coexistence with its vapor phase, which is crucial in wetting and spreading dynamics. Its relation with the i...

Physical Review Letters

Kondo-Induced Giant Isotropic Negative Thermal Expansion

D. G. Mazzone, M. Dzero, AM. M. Abeykoon, H. Yamaoka, H. Ishii, N. Hiraoka, J.-P. Rueff, J. M. Ablett, K. Imura, H. S. Suzuki, J. N. Hancock, and I. Jarrige

Negative thermal expansion is an unusual phenomenon appearing in only a handful of materials, but pursuit and mastery of the phenomenon holds great promise for applications across disciplines and industries. Here we report use of x-ray spectroscopy and diffraction to investigate the $4f$-electronic ...

Physical Review Letters

Ultimate Strength of Metals

Michael Chandross and Nicolas Argibay

The peak strength of a metal occurs when the boundaries between its grains and the grains themselves have the same strength.

Physical Review Letters

Two-Dimensional Antimony Oxide

Stefan Wolff, Roland Gillen, Mhamed Assebban, Gonzalo Abellán, and Janina Maultzsch

Two-dimensional (2D) antimony, so-called antimonene, can form antimonene oxide when exposed to air. We present different types of single- and few-layer antimony oxide structures, based on density functional theory (DFT) calculations. Depending on stoichiometry and bonding type, these novel 2D layers...

Physical Review Letters

Three-Phase Fluid Coexistence in Heterogenous Slits

Martin Láska, Andrew O. Parry, and Alexandr Malijevský

We study the competition between local (bridging) and global condensation of fluid in a chemically heterogeneous capillary slit made from two parallel adjacent walls each patterned with a single stripe. Using a mesoscopic modified Kelvin equation, which determines the shape of the menisci pinned at ...

Physical Review Letters

Intercalated $\mathrm{C}{\mathrm{u}}^{+}$ ion dynamics in the two-dimensional layered compound $\mathrm{C}{\mathrm{u}}_{0.33}\mathrm{TiS}{\mathrm{e}}_{2}$

Shunsuke Kitou, Takumi Hasegawa, Akitoshi Nakano, Naoyuki Katayama, Satoshi Tsutsui, and Hiroshi Sawa

$\mathrm{C}{\mathrm{u}}^{+}$ ion behavior is one of the heavily discussed topics in physical and material fields because of its unclear behavior and high potential in materials application. To provide a breakthrough in this field, comprehensive research that connects the real space and the reciproca...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Tunable Casimir equilibria with phase change materials: From quantum trapping to its release

Lixin Ge, Xi Shi, Zijun Xu, and Ke Gong

A stable suspension of nanoscale particles due to the Casimir force is of great interest for many applications such as sensing, noncontract nanomachines. However, the suspension properties are difficult to change once the devices are fabricated. Vanadium dioxide (${\mathrm{VO}}_{2}$) is a phase chan...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Higher-order topological phases in a spring-mass model on a breathing kagome lattice

Hiromasa Wakao, Tsuneya Yoshida, Hiromu Araki, Tomonari Mizoguchi, and Yasuhiro Hatsugai

We propose a realization of higher-order topological phases in a spring-mass model with a breathing kagome structure. To demonstrate the existence of the higher-order topological phases, we characterize the topological properties and show that the corner states appear under the fixed boundary condit...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Switchable phonon diodes using nonlinear topological Maxwell lattices

Di Zhou, Jihong Ma, Kai Sun, Stefano Gonella, and Xiaoming Mao

Recent progress in topological mechanics has revealed a family of Maxwell lattices that exhibit topologically protected floppy edge modes. These modes lead to a strongly asymmetric elastic wave response. In this paper, we show how topological Maxwell lattices can be used to realize nonreciprocal tra...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Local-structure evidence for a phase transition in a lead-free single crystal of $(\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}\text{−}0.06\mathrm{BaTi}{\mathrm{O}}_{3}$ by absorption fine-structure spectroscopy with synchrotron x-ray radiation

Xiaobing Li, Shengdong Nie, Feifei Wang, Xiangyong Zhao, Haiwu Zhang, Haosu Luo, Guorong Li, Jae-Hyeon Ko, Zhi Guo, Zheng Jiang, and Renzhong Tai

$(\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2})\mathrm{Ti}{\mathrm{O}}_{3}\text{−}x\mathrm{BaTi}{\mathrm{O}}_{3}(\mathrm{NBT}\text{−}x\mathrm{BT})$ single crystal, as one of the most promising candidates to replace lead-based ferroelectrics, is a typical and unique lead-free system with ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Anisotropic character of the metal-to-metal transition in $\mathrm{P}{\mathrm{r}}_{4}\mathrm{N}{\mathrm{i}}_{3}{\mathrm{O}}_{10}$

Shangxiong Huangfu, Gawryluk Dariusz Jakub, Xiaofu Zhang, Olivier Blacque, Pascal Puphal, Ekaterina Pomjakushina, Fabian O. von Rohr, and Andreas Schilling

As a member of the Ruddlesden-Popper $L{n}_{\mathrm{n}+1}\mathrm{N}{\mathrm{i}}_{\mathrm{n}}{\mathrm{O}}_{3\mathrm{n}+1}$ series rare-earth-nickelates, $\mathrm{P}{\mathrm{r}}_{4}\mathrm{N}{\mathrm{i}}_{3}{\mathrm{O}}_{10}$ consists of infinite quasi-two-dimensional perovskite-like Ni-O based layers...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

First-principles melting of krypton and xenon based on many-body relativistic coupled-cluster interaction potentials

O. R. Smits, P. Jerabek, E. Pahl, and P. Schwerdtfeger

The solid-to-liquid phase transition for krypton and xenon is studied by means of parallel-tempering Monte Carlo simulations based on an accurate description of the atomic interactions within a many-body ansatz using relativistic coupled-cluster theory. These high-level data were subsequently fitted...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Charge transport in epitaxial barium titanate films

M. Tyunina and M. Savinov

The electrical conductivity of epitaxial $\mathrm{BaTi}{\mathrm{O}}_{3}$ films was studied by small-signal impedance spectroscopy at temperatures of 10–720 K using Pt-$\mathrm{BaTi}{\mathrm{O}}_{3}−\mathrm{SrRu}{\mathrm{O}}_{3}$ capacitors. The $∼150$-nm-thick $\mathrm{BaTi}{\mathrm{O}}_{3}$ films p...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Structures of solid hydrogen at 300 K

Graeme J. Ackland and John S. Loveday

We present simulated x-ray diffraction patterns (XRD) from molecular dynamics studies of phase transformations in hydrogen at room temperature. Phase changes can be easily identified in simulation, by directly imaging the atoms and measuring correlation functions. We show that the room-temperature X...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Neutron diffraction and symmetry analysis of the martensitic transformation in Co-doped ${\mathrm{Ni}}_{2}\mathrm{MnGa}$

Fabio Orlandi, Aslı Çakır, Pascal Manuel, Dmitry D. Khalyavin, Mehmet Acet, and Lara Righi

Martensitic transformations are strain driven displacive transitions governing the mechanical and physical properties in intermetallic materials. This is the case in ${\mathrm{Ni}}_{2}\mathrm{MnGa}$, where the martensite transition is at the heart of the striking magnetic shape memory and magnetocal...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Nonadiabatic effects and excitonlike states during the insulator-to-metal transition in warm dense hydrogen

Ilya D. Fedorov, Nikita D. Orekhov, and Vladimir V. Stegailov

The transition of molecular hydrogen to atomic ionized state with the increase of temperature and pressure poses still unresolved problems for experimental methods and theory. Here we analyze the dynamics of this transition and show its nonequilibrium nonadiabatic character overlooked in both interp...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Quantum paraelectricity of ${\mathrm{BaFe}}_{12}{\mathrm{O}}_{19}$

Xuefeng Zhang, Qi-Jun Ye, Hongjun Xiang, and Xin-Zheng Li

Using path-integral Monte Carlo sampling and a lattice Wannier function based effective Hamiltonian obtained from first principles, we show that the quantum fluctuations of the nuclei play a central role in the paraelectric phase of ${\text{BaFe}}_{12}{\text{O}}_{19}$ at low temperatures $(T$'s). Co...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Copper, gold, and platinum under femtosecond irradiation: Results of first-principles calculations

N. A. Smirnov

The paper investigates the interaction of femtosecond laser pulses with the thin films of copper, gold, and platinum. It considers electron-phonon relaxation processes and melting in the metal system nonequilibrium heated by laser radiation. Instead of the approximated formula by Wang et al. [Phys. ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Thermodynamics of the insulator-metal transition in dense liquid deuterium

M. P. Desjarlais, M. D. Knudson, and R. Redmer

Recent dynamic compression experiments [M. D. Knudson et al., Science 348, 1455 (2015); P. M. Celliers et al., Science 361, 677 (2018)] have observed the insulator-metal transition in dense liquid deuterium, but with an approximately 95-GPa difference in the quoted pressures for the transition at ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Properties of bulk liquid Pd and Pt and their free liquid surface studied with first principles techniques

Beatriz G del Rio, Luis E González and David J González

We have performed first principles computer simulations in order to study the structural and dynamic properties of bulk liquid Pd and Pt near their melting points. We find good agreement with the available experimental static structure and transport properties, and furthermore we provide more detailed information that is not available from experiments. Additional simulations have also been undertaken so as to study the free liquid surface of both liquid metals. The calculated longitudinal ionic density profile exhibits an oscillatory behavior whose properties have been analyzed. For both metals, the associated intrinsic surface structure factor presents a marked maximum related to surface layering.

Modelling and Simulation in Materials Science and Engineering

Thermodynamic modelling of polycrystalline multicomponent multiphase metal alloys

Antonio Mario Locci, Francesco Torre and Francesco Delogu

The present work explores the thermodynamic stability of multicomponent multiphase polycrystalline metal alloys using a theoretical approach based on the regular solution model. We extend the definition of ‘phase’ to homogeneous bodies of any dimensionality, which allows grain boundaries to take on phase-like, or complexion, properties, with energy and chemical composition different from grain interiors. Accordingly, we examine the possible attainment of structural stability due to grain boundary segregation within the framework of equilibrium thermodynamics, making use of a Gibbs free energy function. We also derive a dimensionless version of the model for greater generality, and to properly compare the factors determining the thermodynamic stability of polycrystalline structures. Model predictions are summarized with the help of suitably defined stability maps and a few case studies concerning binary and ternary alloys are discussed.

Modelling and Simulation in Materials Science and Engineering

Implementation of annihilation and junction reactions in vector density-based continuum dislocation dynamics

Peng Lin and Anter El-Azab

In a continuum dislocation dynamics (CDD) formulation by Xia and El-Azab (2015 Modelling Simul. Mater. Sci. Eng. 23 055009), dislocations are represented by a set of vector density fields, one per crystallographic slip systems. The space-time evolution of these densities is obtained by solving a set of dislocation transport equations coupled with crystal mechanics. Here, we present an approach for incorporating dislocation annihilation and junction reactions into the dislocation transport equations. These reactions consume dislocations and result in nothing as in the annihilation reactions, or produce new dislocations of different types as in the case of junction reactions. Collinear annihilation, glissile junctions, and sessile junctions are particularly emphasized here. A generalized energy-based criterion for junction reactions is established in terms of the dislocation density and Burgers vectors of the reacting species, and the reaction rate terms for junction...

Modelling and Simulation in Materials Science and Engineering

Roadmap on multiscale materials modeling

Erik van der Giessen, Peter A Schultz, Nicolas Bertin, Vasily V Bulatov, Wei Cai, Gábor Csányi, Stephen M Foiles, M G D Geers, Carlos González, Markus Hütter, Woo Kyun Kim, Dennis M Kochmann, Javier LLorca, Ann E Mattsson, Jörg Rottler, Alexander Shluger, Ryan B Sills, Ingo Steinbach, Alejandro Strachan and Ellad B Tadmor

Modeling and simulation is transforming modern materials science, becoming an important tool for the discovery of new materials and material phenomena, for gaining insight into the processes that govern materials behavior, and, increasingly, for quantitative predictions that can be used as part of a design tool in full partnership with experimental synthesis and characterization. Modeling and simulation is the essential bridge from good science to good engineering, spanning from fundamental understanding of materials behavior to deliberate design of new materials technologies leveraging new properties and processes. This Roadmap presents a broad overview of the extensive impact computational modeling has had in materials science in the past few decades, and offers focused perspectives on where the path forward lies as this rapidly expanding field evolves to meet the challenges of the next few decades. The Roadmap offers perspectives on advances within disciplines as diverse as p...

Modelling and Simulation in Materials Science and Engineering

March 16 2020

Tesla-Scale Terahertz Magnetic Impulses

Shawn Sederberg, Fanqi Kong, and Paul B. Corkum

Simulations suggest that a relatively simple laser technique could produce femtosecond magnetic-field pulses, which currently are only available at a few major lab facilities.

Physical Review X

Nucleation of Dislocations in 3.9 nm Nanocrystals at High Pressure

Abhinav Parakh, Sangryun Lee, K. Anika Harkins, Mehrdad T. Kiani, David Doan, Martin Kunz, Andrew Doran, Lindsey A. Hanson, Seunghwa Ryu, and X. Wendy Gu

As circuitry approaches single nanometer length scales, it has become important to predict the stability of single nanometer-sized metals. The behavior of metals at larger scales can be predicted based on the behavior of dislocations, but it is unclear if dislocations can form and be sustained at si...

Physical Review Letters

Measuring Dynamic Structural Changes of Nanoparticles at the Atomic Scale Using Scanning Transmission Electron Microscopy

Annelies De wael, Annick De Backer, Lewys Jones, Aakash Varambhia, Peter D. Nellist, and Sandra Van Aert

We propose a new method to measure atomic scale dynamics of nanoparticles from experimental high-resolution annular dark field scanning transmission electron microscopy images. By using the so-called hidden Markov model, which explicitly models the possibility of structural changes, the number of at...

Physical Review Letters

Role of Thermal Equilibrium Dynamics in Atomic Motion during Nonthermal Laser-Induced Melting

Xiaocui Wang, J. C. Ekström, Å. U. J. Bengtsson, A. Jarnac, A. Jurgilaitis, Van-Thai Pham, D. Kroon, H. Enquist, and J. Larsson

This study shows that initial atomic velocities as given by thermodynamics play an important role in the dynamics of phase transitions. We tracked the atomic motion during nonthermal laser-induced melting of InSb at different initial temperatures. The ultrafast atomic motion following bond breaking ...

Physical Review Letters

March 12 2020

Hard X Rays from Laser-Wakefield Accelerators in Density Tailored Plasmas

Michaela Kozlova, Igor Andriyash, Julien Gautier, Stephane Sebban, Slava Smartsev, Noemie Jourdain, Uddhab Chulagain, Yasmina Azamoum, Amar Tafzi, Jean-Philippe Goddet, Kosta Oubrerie, Cedric Thaury, Antoine Rousse, and Kim Ta Phuoc

The output of a compact x-ray source based on laser-generated plasma can be boosted by tailoring the spatial structure of the plasma.

Physical Review X

Coherence of a Driven Electron Spin Qubit Actively Decoupled from Quasistatic Noise

Takashi Nakajima, Akito Noiri, Kento Kawasaki, Jun Yoneda, Peter Stano, Shinichi Amaha, Tomohiro Otsuka, Kenta Takeda, Matthieu R. Delbecq, Giles Allison, Arne Ludwig, Andreas D. Wieck, Daniel Loss, and Seigo Tarucha

A feedback control technique suppresses low-frequency noise in an electron-spin qubit, boosting coherence time and control fidelity.

Physical Review X

Mode-Locked Topological Insulator Laser Utilizing Synthetic Dimensions

Zhaoju Yang, Eran Lustig, Gal Harari, Yonatan Plotnik, Yaakov Lumer, Miguel A. Bandres, and Mordechai Segev

The unique properties of topological physics allow for the design of an array of synchronized, mutually locked semiconductor laser resonators, which could be used as a source of high-power mode-locked laser pulses.

Physical Review X

Quantum Computing with Rotation-Symmetric Bosonic Codes

Arne L. Grimsmo, Joshua Combes, and Ben Q. Baragiola

A unifying framework for quantum error-correcting codes based on collections of bosons allows for the discovery of new codes that provide robust error correction in line with fundamental theoretical limits.

Physical Review X

Marvels and Pitfalls of the Langevin Algorithm in Noisy High-Dimensional Inference

Stefano Sarao Mannelli, Giulio Biroli, Chiara Cammarota, Florent Krzakala, Pierfrancesco Urbani, and Lenka Zdeborová

A tool for benchmarking one of the algorithms most commonly used in machine-learning provides insight into its performance and could lead to a better theoretical understanding of how similar algorithms work.

Physical Review X

Torque and Angular-Momentum Transfer in Merging Rotating Bose-Einstein Condensates

Toshiaki Kanai, Wei Guo, Makoto Tsubota, and Dafei Jin

When rotating classical fluid drops merge together, angular momentum can be advected from one to another due to the viscous shear flow at the drop interface. It remains elusive what the corresponding mechanism is in inviscid quantum fluids such as Bose-Einstein condensates (BECs). Here we report our...

Physical Review Letters

Symmetry-Protected Topological Triangular Weyl Complex

R. Wang, B. W. Xia, Z. J. Chen, B. B. Zheng, Y. J. Zhao, and H. Xu

Weyl points are often believed to appear in pairs with opposite chirality. In this work, we show by first-principles calculations and symmetry analysis that single Weyl phonons with linear dispersion and double Weyl phonons with quadratic dispersion are simultaneously present between two specific ph...

Physical Review Letters

Nonempirical Free Volume Viscosity Model for Alkane Lubricants under Severe Pressures

Kerstin Falk, Daniele Savio, and Michael Moseler

Viscosities $η$ and diffusion coefficients ${D}_{s}$ of linear and branched alkanes at pressure $0<P<0.7\text{ }\text{ }\mathrm{GPa}$ and temperature $T=500–600\text{ }\text{ }\mathrm{K}$ are calculated from molecular dynamics simulations. Combining Stokes-Einstein, free volume, and random wal...

Physical Review Letters

Meron Spin Textures in Momentum Space

Cheng Guo, Meng Xiao, Yu Guo, Luqi Yuan, and Shanhui Fan

We show that a momentum-space meron spin texture for electromagnetic fields in free space can be generated by controlling the interaction of light with a photonic crystal slab having a nonzero Berry curvature. These spin textures in momentum space have not been previously noted either in electronic ...

Physical Review Letters

Morphological Superfluid in a Nonmagnetic Spin-2 Bose-Einstein Condensate

Emi Yukawa and Masahito Ueda

The two known mechanisms for superflow are the gradient of the U(1) phase and the spin-orbit-gauge symmetry. We find the third mechanism, namely a spatial variation of the order-parameter morphology protected by a hidden su(2) symmetry in a nonmagnetic spin-2 Bose-Einstein condensate. Possible exper...

Physical Review Letters

Phonon Thermal Hall Effect in Strontium Titanate

Xiaokang Li, Benoît Fauqué, Zengwei Zhu, and Kamran Behnia

It has been known for more than a decade that phonons can produce an off-diagonal thermal conductivity in the presence of a magnetic field. Recent studies of thermal Hall conductivity, ${κ}_{xy}$, in a variety of contexts, however, have assumed a negligibly small phonon contribution. We present a st...

Physical Review Letters

Interplay of Chemistry and Faceting at Grain Boundaries in a Model Al Alloy

Huan Zhao, Liam Huber, Wenjun Lu, Nicolas J. Peter, Dayong An, Frédéric De Geuser, Gerhard Dehm, Dirk Ponge, Jörg Neugebauer, Baptiste Gault, and Dierk Raabe

The boundary between two crystal grains can decompose into arrays of facets with distinct crystallographic character. Faceting occurs to minimize the system’s free energy, i.e., when the total interfacial energy of all facets is below that of the topologically shortest interface plane. In a model Al...

Physical Review Letters

Spatial Heterogeneities in Structural Temperature Cause Kovacs’ Expansion Gap Paradox in Aging of Glasses

Matteo Lulli, Chun-Shing Lee, Hai-Yao Deng, Cho-Tung Yip, and Chi-Hang Lam

Volume and enthalpy relaxation of glasses after a sudden temperature change has been extensively studied since Kovacs’ seminal work. One observes an asymmetric approach to equilibrium upon cooling versus heating and, more counterintuitively, the expansion gap paradox, i.e., a dependence on the initi...

Physical Review Letters

Secondary-Phase-Assisted Grain Boundary Migration in ${\mathrm{CuInSe}}_{2}$

Chen Li, Ekin Simsek Sanli, Daniel Barragan-Yani, Helena Stange, Marc-Daniel Heinemann, Dieter Greiner, Wilfried Sigle, Roland Mainz, Karsten Albe, Daniel Abou-Ras, and Peter A. van Aken

Significant structural evolution occurs during the deposition of ${\mathrm{CuInSe}}_{2}$ solar materials when the Cu content increases. We use in situ heating in a scanning transmission electron microscope to directly observe how grain boundaries migrate during heating, causing nondefected grains to...

Physical Review Letters

Critical Slowing Down at the Abrupt Mott Transition: When the First-Order Phase Transition Becomes Zeroth Order and Looks Like Second Order

Satyaki Kundu, Tapas Bar, Rajesh Kumble Nayak, and Bhavtosh Bansal

We report that the thermally induced Mott transition in vanadium sesquioxide shows critical slowing down and enhanced variance (“critical opalescence”) of the order parameter fluctuations measured through low-frequency resistance-noise spectroscopy. Coupled with the observed increase of the phase-or...

Physical Review Letters

Frustration and Atomic Ordering in a Monolayer Semiconductor Alloy

Amin Azizi, Mehmet Dogan, Jeffrey D. Cain, Rahmatollah Eskandari, Xuanze Yu, Emily C. Glazer, Marvin L. Cohen, and Alex Zettl

Frustrated interactions can lead to short-range ordering arising from incompatible interactions of fundamental physical quantities with the underlying lattice. The simplest example is the triangular lattice of spins with antiferromagnetic interactions, where the nearest-neighbor spin-spin interactio...

Physical Review Letters

Intrinsic fracture behavior of Mg–Y alloys

Eleanor Mak and W A Curtin

Pure magnesium (Mg) is an attractive metal for structural applications due to its low density, but also has low ductility and low fracture toughness. Dilute alloying of Mg with rare earth elements in small amounts improves the ductility, but the effects of alloying on fracture are not well-established. Here, the intrinsic fracture of a model Mg-3at%Y solid solution alloy is studied using a combination of anisotropic linear elastic fracture mechanics and atomistic simulations applied to a comprehensive set of crack configurations under mode I loading. The competition between brittle cleavage and ductile dislocation emission at the crack tip in Mg is improved slightly by alloying, because local fluctuations of the random solutes enable dislocation emission rather than cleavage fracture for a number of configurations where the differences in critical load for cleavage and emission are small. However, basal-plane cleavage remains strongly preferred, as in pure Mg. The alloys do show...

Modelling and Simulation in Materials Science and Engineering

Efficient numerical method to handle boundary conditions in 2D elastic media

Dénes Berta, István Groma and Péter Dusán Ispánovity

A numerical method is developed to efficiently calculate the stress (and displacement) field in finite 2D rectangular media. The solution is expanded on a function basis with elements that satisfy the Navier–Cauchy equation. The obtained solution approximates the boundary conditions with their finite Fourier series. The method is capable to handle Dirichlet, Neumann and mixed boundary value problems as well and it was found to converge exponentially fast to the analytical solution with respect to the size of the basis. Possible application in discrete dislocation dynamics simulations is discussed and compared to the widely used finite element methods: it was found that the new method is superior in terms of computational complexity.

Modelling and Simulation in Materials Science and Engineering

An efficient implicit time integration method for discrete dislocation dynamics

Gábor Péterffy and Péter Dusán Ispánovity

Plastic deformation of most crystalline materials is due to the motion of lattice dislocations. Therefore, the simulation of the interaction and dynamics of these defects has become state-of-the-art method to study work hardening, size effects, creep and many other mechanical properties of metallic specimens. Lot of efforts have been made to make the simulations realistic by including specific dislocation mechanisms and the effect of free surfaces. However, less attention has been devoted to the numerical scheme that is used to solve the equations of motion. In this paper we propose a scheme that speeds up simulations by several orders of magnitude. The scheme is implicit because this type is the most efficient one for solving stiff equations that arise due to the long-range nature of dislocation interactions. The numerical results show that the method is not only faster than other approaches at the same numerical precision, but it can also be efficiently applied even without di...

Modelling and Simulation in Materials Science and Engineering

March 05 2020

Photoinduced Nonequilibrium Response in Underdoped ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ Probed by Time-Resolved Terahertz Spectroscopy

S. J. Zhang, Z. X. Wang, H. Xiang, X. Yao, Q. M. Liu, L. Y. Shi, T. Lin, T. Dong, D. Wu, and N. L. Wang

Recent claims of light-induced room-temperature superconductivity in YBa2Cu3O6+x can be explained instead by the generation of quasiparticles, and the observed optical signatures do not require phonon excitation as reported.

Physical Review X

Topological Elasticity of Flexible Structures

Adrien Saremi and Zeb Rocklin

A new elastic theory describes how the microstructures of certain materials can lead to large, abrupt deformations whose origin cannot be explained with standard models.

Physical Review X

Parity Detection of Propagating Microwave Fields

Jean-Claude Besse, Simone Gasparinetti, Michele C. Collodo, Theo Walter, Ants Remm, Jonas Krause, Christopher Eichler, and Andreas Wallraff

An experiment that can distinguish between an even or odd number of photons in a microwave pulse could lead to a versatile tool for identifying errors in quantum communication channels.

Physical Review X

Fast High-Fidelity Quantum Nondemolition Qubit Readout via a Nonperturbative Cross-Kerr Coupling

R. Dassonneville, T. Ramos, V. Milchakov, L. Planat, É. Dumur, F. Foroughi, J. Puertas, S. Leger, K. Bharadwaj, J. Delaforce, C. Naud, W. Hasch-Guichard, J. J. García-Ripoll, N. Roch, and O. Buisson

A new qubit readout scheme preserves quantum state probabilities while maximizing fidelity with a fast readout time, thus providing a robust measurement method for a new generation of superconducting quantum processors.

Physical Review X

Critical Switching in Globally Attractive Chimeras

Yuanzhao Zhang, Zachary G. Nicolaou, Joseph D. Hart, Rajarshi Roy, and Adilson E. Motter

Newly discovered stochastic switching in networks exhibits anomalous scaling and extreme sensitivity to noise.

Physical Review X

Subdiffusion and Heat Transport in a Tilted Two-Dimensional Fermi-Hubbard System

Elmer Guardado-Sanchez, Alan Morningstar, Benjamin M. Spar, Peter T. Brown, David A. Huse, and Waseem S. Bakr

Experiments show that a particular quantum many-body system thermalizes surprisingly slowly, and a hydrodynamic model of the system reveals a crucial underlying link between the transport of both mass and heat.

Physical Review X

Long-Range Prethermal Phases of Nonequilibrium Matter

Francisco Machado, Dominic V. Else, Gregory D. Kahanamoku-Meyer, Chetan Nayak, and Norman Y. Yao

The existence of prethermal phases of matter in long-range interacting systems is remarkably robust, opening the door to the experimental realization of a novel, disorder-free, prethermal discrete time crystal in 1D.

Physical Review X

Direct Comparison of Many-Body Methods for Realistic Electronic Hamiltonians

Kiel T. Williams, Yuan Yao, Jia Li, Li Chen, Hao Shi, Mario Motta, Chunyao Niu, Ushnish Ray, Sheng Guo, Robert J. Anderson, Junhao Li, Lan Nguyen Tran, Chia-Nan Yeh, Bastien Mussard, Sandeep Sharma, Fabien Bruneval, Mark van Schilfgaarde, George H. Booth, Garnet Kin-Lic Chan, Shiwei Zhang, Emanuel Gull, Dominika Zgid, Andrew Millis, Cyrus J. Umrigar, and Lucas K. Wagner (Simons Collaboration on the Many-Electron Problem)

Tests of over 20 techniques for approximating many-body electron systems reveal which approaches are best suited to accurate modeling of these systems.

Physical Review X

Observation of a Charge-Neutral Muon-Polaron Complex in Antiferromagnetic ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$

M. H. Dehn, J. K. Shenton, S. Holenstein, Q. N. Meier, D. J. Arseneau, D. L. Cortie, B. Hitti, A. C. Y. Fang, W. A. MacFarlane, R. M. L. McFadden, G. D. Morris, Z. Salman, H. Luetkens, N. A. Spaldin, M. Fechner, and R. F. Kiefl

Experiments reveal muon-polaron complexes in Cr2O3. Similar entities may exist in many magnetic insulators and semiconductors, where they can be used as proxies to understand the impact of hydrogen impurities.

Physical Review X

Optimal Renormalization Group Transformation from Information Theory

Patrick M. Lenggenhager, Doruk Efe Gökmen, Zohar Ringel, Sebastian D. Huber, and Maciej Koch-Janusz

A new approach to developing real-space renormalization group methods paves the way for using machine learning to derive large-scale behavior of physical systems from microscopic models.

Physical Review X

Spin-Orbital-Intertwined Nematic State in FeSe

J. Li, B. Lei, D. Zhao, L. P. Nie, D. W. Song, L. X. Zheng, S. J. Li, B. L. Kang, X. G. Luo, T. Wu, and X. H. Chen

A new quantum state of matter in an FeSe superconductor arises from the interplay between electron correlation and spin-orbit coupling, cementing this material family as a solid platform for exploring connections between these two fundamental interactions.

Physical Review X

Nematic State in ${\mathrm{CeAuSb}}_{2}$

S. Seo, Xiaoyu Wang, S. M. Thomas, M. C. Rahn, D. Carmo, F. Ronning, E. D. Bauer, R. D. dos Reis, M. Janoschek, J. D. Thompson, R. M. Fernandes, and P. F. S. Rosa

The discovery of a vestigial nematic electronic phase in CeAuSb2 without superconductivity reveals the complex interplay between this phase and stripe magnetic order and how this interplay relates to high-temperature superconductivity.

Physical Review X

Modular Arithmetic with Nodal Lines: Drumhead Surface States in ZrSiTe

Lukas Muechler, Andreas Topp, Raquel Queiroz, Maxim Krivenkov, Andrei Varykhalov, Jennifer Cano, Christian R. Ast, and Leslie M. Schoop

Experiments reveal so-called drumhead surface states in a well-studied family of nodal semimetals, unraveling the complex interplay between different types of surface states in a complex class of materials.

Physical Review X

Atomically Resolved Chemical Reactivity of Small Fe Clusters

Julian Berwanger, Svitlana Polesya, Sergiy Mankovsky, Hubert Ebert, and Franz J. Giessibl

Using a scanning probe microscope, researchers measure the dependence of an atom’s chemical reactivity on the number of chemical bonds it forms.

Physical Review Letters

Ab initio Determination of the Phase Diagram of ${\mathrm{CO}}_{2}$ at High Pressures and Temperatures

Beatriz H. Cogollo-Olivo, Sananda Biswas, Sandro Scandolo, and Javier A. Montoya

The experimental study of the ${\mathrm{CO}}_{2}$ phase diagram is hampered by strong kinetic effects leading to wide regions of metastability and to large uncertainties in the location of some phase boundaries. Here, we determine ${\mathrm{CO}}_{2}$’s thermodynamic phase boundaries by means of ab i...

Physical Review Letters

Shear Softening in a Metallic Glass: First-Principles Local-Stress Analysis

I. Lobzenko, Y. Shiihara, T. Iwashita, and T. Egami

Metallic glasses deform elastically under stress. However, the atomic-level origin of elastic properties of metallic glasses remain unclear. In this Letter using ab initio molecular dynamics simulations of the ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ metallic glass under shear strain, we show that the...

Physical Review Letters

Efficient Global Structure Optimization with a Machine-Learned Surrogate Model

Malthe K. Bisbo and Bjørk Hammer

We propose a scheme for global optimization with first-principles energy expressions of atomistic structure. While unfolding its search, the method actively learns a surrogate model of the potential energy landscape on which it performs a number of local relaxations (exploitation) and further struct...

Physical Review Letters

Self-Learning Method for Construction of Analytical Interatomic Potentials to Describe Laser-Excited Materials

Bernd Bauerhenne, Vladimir P. Lipp, Tobias Zier, Eeuwe S. Zijlstra, and Martin E. Garcia

Large-scale simulations using interatomic potentials provide deep insight into the processes occurring in solids subject to external perturbations. The atomistic description of laser-induced ultrafast nonthermal phenomena, however, constitutes a particularly difficult case and has so far not been po...

Physical Review Letters

Shear Controls Frictional Aging by Erasing Memory

Sam Dillavou and Shmuel M. Rubinstein

We simultaneously measure the static friction and the real area of contact between two solid bodies. These quantities are traditionally considered equivalent, and under static conditions both increase logarithmically in time, a phenomenon coined aging. Here we show that the frictional aging rate is ...

Physical Review Letters

Deterministic Scheme for Two-Dimensional Type-II Dirac Points and Experimental Realization in Acoustics

Xiaoxiao Wu, Xin Li, Ruo-Yang Zhang, Xiao Xiang, Jingxuan Tian, Yingzhou Huang, Shuxia Wang, Bo Hou, C. T. Chan, and Weijia Wen

Low-energy electrons near Dirac/Weyl nodal points mimic massless relativistic fermions. However, as they are not constrained by Lorentz invariance, they can exhibit tipped-over type-II Dirac/Weyl cones that provide highly anisotropic physical properties and responses, creating unique possibilities. ...

Physical Review Letters

Stress-Measure Dependence of Phase Transformation Criterion under Finite Strains: Hierarchy of Crystal Lattice Instabilities for Homogeneous and Heterogeneous Transformations

Hamed Babaei and Valery I. Levitas

Hierarchy of crystal lattice instabilities leading to a first-order phase transformation (PT) is found, which consists of PT instability described by the order parameter and elastic instabilities under different prescribed stress measures. After PT instability and prior to the elastic instability, a...

Physical Review Letters

Why Phonon Scattering in Glasses is Universally Small at Low Temperatures

Herve M. Carruzzo and Clare C. Yu

We present a novel view of the standard model of tunneling two level systems (TLSs) to explain the puzzling universal value of a quantity, $C∼3×{10}^{−4}$, that characterizes phonon scattering in glasses below 1 K as reflected in thermal conductivity, ultrasonic attenuation, internal friction, and t...

Physical Review Letters

Nucleation and Growth of the Supercooled Liquid Phase Control Glass Transition in Bulk Ultrastable Glasses

A. Vila-Costa, J. Ràfols-Ribé, M. González-Silveira, A. F. Lopeandia, Ll. Abad-Muñoz, and J. Rodríguez-Viejo

We report the anomalous bulk transformation of vapor deposited stable glasses into the liquid state. The transformation proceeds through two competing parallel processes: partial rejuvenation of the stable glass and nucleation and growth of liquid patches within the glass. The kinetics of the transf...

Physical Review Letters

Effect of He on the Order-Disorder Transition in ${\mathrm{Ni}}_{3}\mathrm{Al}$ under Irradiation

Peyman Saidi, Pooyan Changizian, Eric Nicholson, He Ken Zhang, Yu Luo, Zhongwen Yao, Chandra Veer Singh, Mark R. Daymond, and Laurent Karim Béland

The order-disorder transition in Ni-Al alloys under irradiation represents an interplay between various reordering processes and disordering due to thermal spikes generated by incident high energy particles. Typically, ordering is enabled by diffusion of thermally generated vacancies, and can only t...

Physical Review Letters

Particlelike Phonon Propagation Dominates Ultralow Lattice Thermal Conductivity in Crystalline ${\mathrm{Tl}}_{3}{\mathrm{VSe}}_{4}$

Yi Xia, Koushik Pal, Jiangang He, Vidvuds Ozoliņš, and Chris Wolverton

We investigate the microscopic mechanisms of ultralow lattice thermal conductivity (${κ}_{l}$) in ${\mathrm{Tl}}_{3}{\mathrm{VSe}}_{4}$ by combining a first principles density functional theory based framework of anharmonic lattice dynamics with the Peierls-Boltzmann transport equation for phonons. ...

Physical Review Letters

Lone Pair Rotational Dynamics in Solids

Richard C. Remsing and Michael L. Klein

Traditional classifications of crystalline phases focus on nuclear degrees of freedom. Through the examination of both electronic and nuclear structure, we introduce the concept of an electronic plastic crystal. Such a material is classified by crystalline nuclear structure, while localized electron...

Physical Review Letters

Mean Inner Potential of Liquid Water

Murat Nulati Yesibolati, Simone Laganà, Hongyu Sun, Marco Beleggia, Shawn M. Kathmann, Takeshi Kasama, and Kristian Mølhave

Improving our experimental and theoretical knowledge of electric potentials at liquid-solid boundaries is essential to achieve a deeper understanding of the driving forces behind interfacial processes. Electron holography has proved successful in probing solid-solid interfaces but requires knowledge...

Physical Review Letters

Universal Scaling of the Velocity Field in Crack Front Propagation

Clément Le Priol, Julien Chopin, Pierre Le Doussal, Laurent Ponson, and Alberto Rosso

The propagation of a crack front in disordered materials is jerky and characterized by bursts of activity, called avalanches. These phenomena are the manifestation of an out-of-equilibrium phase transition originated by the disorder. As a result avalanches display universal scalings which are, howev...

Physical Review Letters

Rounded Layering Transitions on the Surface of Ice

Pablo Llombart, Eva G. Noya, David N. Sibley, Andrew J. Archer, and Luis G. MacDowell

Understanding the wetting properties of premelting films requires knowledge of the film’s equation of state, which is not usually available. Here we calculate the disjoining pressure curve of premelting films and perform a detailed thermodynamic characterization of premelting behavior on ice. Analys...

Physical Review Letters

Coalescence of Au Nanoparticles without Ligand Detachment

Pan Guo and Yi Gao

Repulsion of ligands is known as the key factor for hindering nanoparticle (NP) coalescence. Thus, during the past decade, it has generally accepted that the full removal of capping ligands of the contact surface is the first step for NP coalescence. Herein, using molecular dynamics simulations, we ...

Physical Review Letters

Decompression-Induced Diamond Formation from Graphite Sheared under Pressure

Jiajun Dong, Zhen Yao, Mingguang Yao, Rui Li, Kuo Hu, Luyao Zhu, Yan Wang, Huanhuan Sun, Bertil Sundqvist, Ke Yang, and Bingbing Liu

Graphite is known to transform into diamond under dynamic compression or under combined high pressure and high temperature, either by a concerted mechanism or by a nucleation mechanism. However, these mechanisms fail to explain the recently reported discovery of diamond formation during ambient temp...

Physical Review Letters

Finite-size effects in lead scandium tantalate relaxor thin films

Abel Fernandez, Jieun Kim, Derek Meyers, Sahar Saremi, and Lane W. Martin

Relaxor ferroelectrics exhibit large electromechanical effects in response to external stimuli, making them promising materials for a variety of energy-harvesting, sensing, and actuating applications. An open question in the field, however, is how the polarization response evolves when the sample size approaches the nanometer length scale of polar correlations. Here, the evolution of polarization response as a function of film thickness is studied in epitaxial thin films of the relaxor lead scandium tantalate, demonstrating a large suppression of polarization response at reduced thickness.

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Topological nonmagnetic impurity states in topological Kondo insulators

M. Abele, X. Yuan, and P. S. Riseborough

We examine the presence of nonmagnetic impurities in a hybridization gap model of a Kondo insulator which has band inversion. The model has been used to predict that ${\mathrm{SmB}}_{6}$ is a topological insulator. We show that there are two types of nonmagnetic impurity states in a Kondo insulator....

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Reducing lead toxicity in the methylammonium lead halide ${\mathrm{MAPbI}}_{3}$: Why Sn substitution should be preferred to Pb vacancy for optimum solar cell efficiency

Pooja Basera, Manish Kumar, Shikha Saini, and Saswata Bhattacharya

Methylammonium lead halide $({\mathrm{MAPbI}}_{3})$ perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead toxicity, the role of Sn substitution and Pb vacancy (Pb-$⊠)$ are addressed in regulating stability and solar cell efficiency of ${\mathrm{MAPb}}_{1−X−Y}{\ma...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Rotational stability of twisted bilayer graphene

S. Bagchi, H. T. Johnson, and H. B. Chew

Moiré superlattices form in twisted graphene bilayers due to periodic regions of commensurability, but truncation of the moiré patterns affects the rotational stability of finite-sized sheets. Here, we report the stepwise untwisting of nanometer-sized bilayer graphene flakes at elevated temperatures...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Origin of sawtooth domain walls in ferroelectrics

J. Zhang, Y.-J. Wang, J. Liu, J. Xu, D. Wang, L. Wang, X.-L. Ma, C.-L. Jia, and L. Bellaiche

Domains and domain walls are among the key factors that determine the performance of ferroelectric materials. In recent years, a unique type of domain walls, i.e., the sawtooth-shaped domain walls, has been observed in ${\mathrm{BiFeO}}_{3}$ and ${\mathrm{PbTiO}}_{3}$. Here, we build a minimal model...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Observation of superconductivity accompanying the pressure-induced structural phase transition in LaSb

Min Zhang, Xiangqi Wang, Azizur Rahman, Rucheng Dai, Zhongping Wang, and Zengming Zhang

LaSb has attracted intense interest due to the recent discovery of its extreme magnetoresistance (XMR) and controversial topology states. Motivated by the existing structural phase transition and the possible topological phase transition, the electrical transport properties of a LaSb single crystal ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Rotational intersite displacement of disordered lead atoms in a relaxor ferroelectric during piezoelectric lattice straining and ferroelectric domain switching

Shinobu Aoyagi, Ayumi Aoyagi, Hitoshi Osawa, Kunihisa Sugimoto, Yuki Nakahira, Chikako Moriyoshi, Yoshihiro Kuroiwa, and Makoto Iwata

We report results of the time-resolved x-ray structure analysis of a relaxor ferroelectric single crystal under an alternating electric field. The time dependence of the lattice strain, atomic displacements, and ferroelectric domain volumes in a $0.955\mathrm{Pb}(\mathrm{Z}{\mathrm{n}}_{1/3}\mathrm{...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Crystal structure and magnetism of MnO under pressure

S. Klotz, K. Komatsu, A. Polian, S. Machida, A. Sano-Furukawa, J.-P. Itié, and T. Hattori

Manganese oxide is a prototype of an antiferromagnetic Mott insulator. Here, we investigate the interplay of magnetic ordering and lattice distortion across the Néel temperature ${T}_{N}$ under pressure using neutron and x-ray diffraction. We find an increase in ${T}_{N}$ with a rate of $d{T}_{N}/dP...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Correlation between the composition-dependent properties and phase stability of ${\mathrm{Co}}_{2}Y\text{Ga}\phantom{\rule{4pt}{0ex}}(Y=\text{Cr},\text{V})$ shape-memory alloys from first-principles study

Chun-Mei Li, Yang Zhang, Wen-Jiang Feng, Ren-Zhong Huang, and Ming Gao

The composition-dependent properties and phase stability of ${\mathrm{Co}}_{2}\phantom{\rule{4pt}{0ex}}Y\text{Ga}\phantom{\rule{4pt}{0ex}}(Y=\text{Cr},\text{V})$-based shape-memory alloys are investigated by using the first-principles exact muffin-tin-orbital method in combination with the coherent ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Acoustic metamaterials with spinning components

Degang Zhao, Yao-Ting Wang, Kin-Hung Fung, Zhao-Qing Zhang, and C. T. Chan

We show that an acoustic metamaterial consisting of an array of spinning cylindrical inclusions can possess many unusual properties, including folded bulk bands and interface-state bands. The folding of bands inside the first Brillouin zone is made possible by a rotation-induced antiresonance of com...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

${\mathrm{Ca}}_{3}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ structural path unraveled by atomic-scale properties: A combined experimental and ab initio study

P. Rocha-Rodrigues, S. S. M. Santos, I. P. Miranda, G. N. P. Oliveira, J. G. Correia, L. V. C. Assali, H. M. Petrilli, J. P. Araújo, and A. M. L. Lopes

The structural phase transition path from the low-temperature polar structure up to the highest symmetric phase in the hybrid improper ferroelectric ${\mathrm{Ca}}_{3}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ compound is here investigated at atomic scale. Measurements using the perturbed angular correlatio...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Scaling behavior of low-temperature orthorhombic domains in the prototypical high-temperature superconductor ${\mathrm{La}}_{1.875}{\mathrm{Ba}}_{0.125}{\mathrm{CuO}}_{4}$

T. A. Assefa, Y. Cao, J. Diao, R. J. Harder, W. Cha, K. Kisslinger, G. D. Gu, J. M. Tranquada, M. P. M. Dean, and I. K. Robinson

Structural symmetry breaking and recovery in condensed-matter systems are closely related to exotic physical properties such as superconductivity (SC), magnetism, spin density waves, and charge density waves (CDWs). The interplay between different order parameters is intricate and often subject to i...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Elastic-frustration-driven unusual magnetoelastic properties in a switchable core-shell spin-crossover nanostructure

Yogendra Singh, Hassane Oubouchou, Masamichi Nishino, Seiji Miyashita, and Kamel Boukheddaden

Spin-crossover (SCO) solids have been studied for their fascinating properties, exhibiting first-order phase transitions and macroscopic bistabilities, accompanied by significant magnetic, structural, and optical changes. These exceptional properties make these materials promising for applications a...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Electron heating and mechanical properties of graphene

Jose Angel Silva-Guillén and Francisco Guinea

The heating of electrons in graphene by laser irradiation, and its effects on the lattice structure, are studied. Values for the temperature of the electron system in realistic situations are obtained. For sufficiently high electron temperatures, the occupancy of the states in the $σ$ band of graphe...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Optimization of power broadening in optically detected magnetic resonance of defect spins in silicon carbide

Jun-Feng Wang, Jin-Ming Cui, Fei-Fei Yan, Qiang Li, Ze-Di Cheng, Zheng-Hao Liu, Zhi-Hai Lin, Jin-Shi Xu, Chuan-Feng Li, and Guang-Can Guo

Defect spins in silicon carbide have become promising platforms with respect to quantum information processing and quantum sensing. Indeed, the optically detected magnetic resonance (ODMR) of defect spins is the cornerstone of the applications. In this work, we systematically investigate the contras...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Layer dependence of defect charge transition levels in two-dimensional materials

Dan Wang and Ravishankar Sundararaman

Point defects in two-dimensional (2D) materials hold great promise for optoelectronic and quantum technologies. Their properties depend sensitively on the dielectric environment and number of 2D layers, but this has remained a challenge to include in first-principles calculations on account of the h...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Unusual charge density wave transition and absence of magnetic ordering in ${\mathrm{Er}}_{2}{\mathrm{Ir}}_{3}{\mathrm{Si}}_{5}$

Sitaram Ramakrishnan, Andreas Schönleber, Toms Rekis, Natalija van Well, Leila Noohinejad, Sander van Smaalen, Martin Tolkiehn, Carsten Paulmann, Biplab Bag, Arumugam Thamizhavel, Dilip Pal, and Srinivasan Ramakrishnan

The first-order charge density wave (CDW) phase transition of ${\mathrm{Er}}_{2}{\mathrm{Ir}}_{3}{\mathrm{Si}}_{5}$ is characterized by a crystal structure analysis, and electrical resistivity, magnetic susceptibility and specific heat measurements. The incommensurate CDW is accompanied by a strong ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Lattice dynamics and structural transition of the hyperhoneycomb iridate $β−{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ investigated by high-pressure Raman scattering

Sungkyun Choi, Heung-Sik Kim, Hun-Ho Kim, Aleksandra Krajewska, Gideok Kim, Matteo Minola, Tomohiro Takayama, Hidenori Takagi, Kristjan Haule, David Vanderbilt, and Bernhard Keimer

We report a polarized Raman scattering study of the lattice dynamics of $β−{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ under hydrostatic pressures up to 7.62 GPa. At ambient pressure, $β−{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ exhibits the hyperhoneycomb crystal structure and a magnetically ordered state of s...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Tungsten migration energy barriers for surface diffusion: a parameterization for KMC simulations

Ville Jansson, Andreas Kyritsakis, Simon Vigonski, Ekaterina Baibuz, Vahur Zadin, Alvo Aabloo and Flyura Djurabekova

We have calculated the migration barriers for surface diffusion on tungsten. Our results form a self-sufficient parameterisation for kinetic Monte Carlo simulations of arbitrarily rough atomic tungsten surfaces, as well as nanostructures such as nanotips and nanoclusters. The parameterisation includes first- and second-nearest neighbour atom jump processes, as well as a third-nearest neighbour exchange process. The migration energy barriers of all processes are calculated with the nudged elastic band method. The same attempt frequency for all processes is found sufficient and the value is fitted to molecular dynamics simulations. The model is validated by correctly simulating with kinetic Monte Carlo the energetically favourable W nanocluster shapes, in good agreement with molecular dynamics simulations.

Modelling and Simulation in Materials Science and Engineering

Microchemistry-dependent simulation of yield stress and flow stress in non-heat treatable Al sheet alloys

Su Leen Wong, Galyna Laptyeva, Thiemo Brüggemann, Olaf Engler, Franz Roters, Dierk Raabe and Kai-Friedrich Karhausen

A flow stress model which considers the processing conditions for a given alloy composition as well as the microchemistry of the alloy allows for integrated optimization of alloy composition, thermal treatments and forming operations to achieve the desired properties in the most efficient processing route. In the past, a statistical flow stress model for cell forming metals, 3IVM+ (3 Internal Variable Model), has been used for through process modeling of sheet production. However, this model was restricted to a given alloy in the state in which it was calibrated. In this work, the existing 3IVM+ model is augmented with an analytical solute strengthening model which uses input from ab initio simulations. Furthermore, a new particle strengthening model for non-shearable precipitates has been introduced which takes Orowan looping at low temperatures and dislocation climb at high temperatures into account. Hence, the present modeling approach considers the strengthening contr...

Modelling and Simulation in Materials Science and Engineering

Three-point bending analysis with cohesive surface interaction for improved delamination prediction and application of carbon fibre reinforced plastics composites

Patrick Hale and Eu-Gene Ng

Carbon fibre reinforced plastics laminates were loaded through to fracture in a three-point bending configuration, to gain understanding of the cohesive interaction between plies and validate mechanical properties and predictive capability of the FE model. The effect of mesh refinement, scaling techniques, failure models and cohesive surfaces were investigated. Fibre orientations investigated were parallel, 45° and perpendicular to the loading. Experimental results showed a larger radius punch promoted failure on the intended bottom side, tensile stresses region, allowing for the Aramis strain camera to record the failure. When the fibre orientation was perpendicular to the punch load, all failure models show similar rate of force increment with respect to displacement. No difference in failure prediction is observed for the different 0° models, except for a 4.18% under prediction by LaRC02 compared to the experiment. With fibre orientations at 45° and 90°, the Maximum Strain an...

Modelling and Simulation in Materials Science and Engineering

Dislocation dynamics in polycrystalline materials

Jaehyun Cho, Joshua C Crone, Athanasios Arsenlis and Sylvie Aubry

An extension of the dislocation dynamics method to polycrystalline materials is presented with emphasis on handling interactions between dislocations and grain boundaries. The key new features of the method include: (1) a grain boundary detection algorithm, (2) new dislocation emission criteria based on power dissipation and area growth, (3) mobility of dislocations at grain boundaries, and (4) extension of topological operations e.g. mesh adaption, collision, and dissociation to handle dislocations interacting with grain boundaries. Verification and validation examples are executed to compare our calculations with existing analytic methods, molecular dynamics simulations, and experimental observations.

Modelling and Simulation in Materials Science and Engineering

Computer simulation of local microstructure and dynamics in aluminum-silicate melt

L T Vinh, P K Hung, To Ba Van and N V Hong

We have investigated the aluminum-silicate melt used as a simple case for many-component network-forming liquids. Based on the calculation of T–O subnets, T–O bonds (T is Si or Al) and commuting linkages, a systematic analysis is carried out to clarifying specific features of microstructure and dynamics. The simulation reveals a strong correlation between the mean square displacements and number of T–O bonds which remain unbroken during the simulation time. The model contains T–O subnets which behave like large molecules. We also find that most mobile and immobile atoms tend to gather in large clusters, the number of which slightly changes during the simulation time. In contrast, the atoms randomly taken from the system form numerous small clusters. The simulation result clearly demonstrates the micro-segregation and strong heterogeneity in dynamics and structure. In particular, the breaking and forming of T–O bonds (the replacing of T–O bonds by new ones) happen non-uniformly t...

Modelling and Simulation in Materials Science and Engineering

February 06 2020

Angular dependence and thermal stability of coercivity of Nd-rich Ga-doped Nd–Fe–B sintered magnet

J. Li, Xin Tang, H. Sepehri-Amin, T.T. Sasaki, T. Ohkubo, K. Hono

Image, graphical abstractWe studied the angular dependence and thermal stability of coercivity of Nd-rich Ga-doped Nd–Fe–B sintered magnets. Experimentally measured angular dependence of coercivity for the as-sintered magnet agrees well with the micromagnetic simulation results for exchange-coupled polycrystalline model that assumes the magnetization reversal is dominated by the domain wall depinning at the grain boundaries. On the other hand, the measured angular dependence of coercivity of the post-sinter annealed sample with an enhanced coercivity deviates from fully exchange-decoupled model in spite of previous experimental results on inter-grain exchange decoupling. Based on micromagnetic simulations and Kronmüller equation, it is suggested that the entire elimination of magnetic exchange coupling between Nd2Fe14B grains can further improve the coercivity and its thermal stability of the 5 µm-grain-sized Dy-free magnet.

Acta Materialia

Instabilities in the periodic arrangement of elastically interacting precipitates in nickel-base superalloys

M. Degeiter, Y. Le Bouar, B. Appolaire, M. Perrut, A. Finel

Graphical abstract for this articleNickel-base superalloys display cuboidal precipitates aligned along the cubic directions, which are the elastic soft directions. At high precipitate volume fraction, the microstructure is often described as a regular array of precipitates organized on a simple cubic macro-lattice. In the present work, we use a stability analysis and 3D phase field simulations to show that such a regular array is in fact unstable whatever the volume fraction of precipitates. The two main instability modes are the longitudinal [100] mode and the transverse [110] mode along the [11¯0] eigenvector. We argue that these instabilities lead to formation of configurational defects closely related to experimentally observed branches and herringbone patterns. The rôles of elastic anisotropy and elastic homogeneity are also discussed.

Acta Materialia

Giant current performance in lead-free piezoelectrics stem from local structural heterogeneity

Xiaodong Yan, Mupeng Zheng, Xin Gao, Mankang Zhu, Yudong Hou

Image, graphical abstractPiezoelectric materials, which convert mechanical vibration energy into electric energy, are essential for vibration energy harvester. Nevertheless, the piezoelectric energy harvesting also encounters the bottleneck that piezoelectric materials generally produce only micro scale current due to its high impedance. In this work, the developed lead-free (Ba0.85Ca0.15)0.9985Sm0.001(Ti0.9Zr0.1)O3 (BCSm0.001TZ) piezoelectric ceramic possesses both high piezoelectric charge constant and low impedance, boosting its energy harvesting performance: an extremely high short-circuit current (60 µA) and large power density (2.1 µW/mm3) in a cantilever-type energy harvester, which is superior to those of other reported ones. Due to the giant current performance, the related charging speed of BCSm0.001TZ energy harvester possessed ~100% enhancement relative to the non-doped counterpart. Electrical property measurement and nanostructure observation revealed that the outstanding electromechanical properties as well as energy harvesting performances in BCSm0.001TZ ceramic benefits from a complex domain architecture and low concentration of defect, which is closely associated with the local structural heterogeneity induced by the rare-earth Sm doping. This work provides a new important paradigm for developing high-performance viable green energy materials and devices, especially for the fast recharging microelectronic storage devices in wireless sensor network.

Acta Materialia

Charged domain wall modulation of resistive switching with large ON/OFF ratios in high density BiFeO 3 nano-islands

M.J. Han, Y.L. Tang, Y.J. Wang, Y.L. Zhu, J.Y. Ma, W.R. Geng, Y.P. Feng, M.J. Zou, N.B. Zhang, X.L. Ma

Image, graphical abstractFerroelectrics exhibit polarization tunable resistance switching behaviors, which are promising for next-generation non-volatile memory devices. For technological applications, thinner nanoscale arrays are expected, which feature with higher density and larger ON/OFF (RON/OFF) ratios in the metal/ferroelectrics/semiconductor heterojunction. Here, we acquire high density BiFeO3 (BFO) nano-islands around 10 nm in thickness displaying a high RON/OFF ratio of 103, comparable to the tunnel junctions. Moreover, both the macroscopic and microscopic resistive switching behaviors of the present BFO films reveal an unexpected filamentary-type resistive switching which is modified by the charged domain walls in nano-islands dominated by the center-type domains. Particularly, the charged domain walls spontaneously formed within the BFO nano-islands are proposed as the conductive paths based on the redistribution of carriers under the applied voltages. Potential applications for memories with large RON/OFF ratios of such kind of configurable charged domain walls are demonstrated.

Acta Materialia

Insight into Si poisoning on grain refinement of Al-Si/Al-5Ti-B system

Yang Li, Bin Hu, Bin Liu, Anmin Nie, Qinfen Gu, Jianfeng Wang, Qian Li

Image, graphical abstractSi poisoning on Al-5Ti-B master alloys has been restraining the effectiveness of grain refinement of hypoeutectic Al-Si casting alloys for over 60 years, and yet the underlying mechanism of this phenomenon remains unclear. In this work, Si poisoning in Al-Si/Al-5Ti-B system was systematically investigated by combining state-of-the-art electron microscopy, first-principles calculations and thermodynamic calculations. Different from the common belief that silicides coat and therefore poison TiB2, this study demonstrates that the segregation of Si atoms at the TiB2/α-Al interface is likely the cause of Si poisoning. Silicide was found to be thermodynamically unfavorable to form even in an alloy with 10 wt.%Si. On the other hand, an appreciable amount of Si (5–20 at.%) was found to segregate in the TiAl3 two-dimensional compound (2DC) which is critical for triggering the nucleation of α-Al on TiB2. The formation of Ti-Si covalent bond within TiAl3 2DC disturbs its lattice and reduces its chemical interaction with α-Al, which both obstruct the epitaxial nucleation of α-Al and hence leads to Si poisoning. This study suggests that composition engineering of TiAl3 2DC and TiB2 with elements less attractive to Si could be a viable way to mitigate Si poisoning.

Acta Materialia

Effect of heterostructure and hetero-deformation induced hardening on the strength and ductility of brass

X.T. Fang, G.Z. He, C. Zheng, X.L. Ma, D. Kaoumi, Y.S. Li, Y.T. Zhu

Image, graphical abstractHeterostructured materials have been reported to possess superior combinations of strength and ductility, which is attributed to hetero-deformation induced (HDI) strengthening and work hardening. However, the influence of heterostructural parameters on the evolution of HDI stress and mechanical behavior during tensile deformation is not well understood. In this paper, heterostructured brass (Cu–30%Zn) was fabricated by cold rolling and partial annealing, to produce heterostructures with different heterostructural parameters, including domain volume fraction, domain thickness/spacing and domain misorientation. It was found that HDI hardening was dominant when the tensile strain was less than ∼4.5%, while conventional dislocation hardening became more effective at higher strain levels. Quick accumulation of geometrically necessary dislocations was found in the domain boundary regions, leading to high HDI stress. Higher domain misorientation was found more effective in developing HDI hardening. These findings elucidate the effect of heterostructure on strength and ductility, which can help with the design of heterostructured materials for superior mechanical properties.

Acta Materialia

The combined effects of hydrogen and aging condition on the deformation and fracture behavior of a precipitation-hardened nickel-base superalloy

Zachary D. Harris, Jishnu J. Bhattacharyya, Joseph A. Ronevich, Sean R. Agnew, James T. Burns

Image, graphical abstractThe effect of hydrogen (H) on the deformation behavior of Monel K-500 in various isothermal heat treatment conditions (non-aged, under-aged, peak-aged, and over-aged) was assessed via uniaxial mechanical testing. H-charged and non-charged specimens were strained to failure to facilitate a comparison of ductility, fracture surface morphology, strength, and work hardening behavior. For all examined heat treatment conditions, H charging leads to a significant reduction in ductility, which is accompanied by a consistent change in fracture surface morphology from ductile microvoid coalescence to brittle intergranular fracture. While H charging led to a systematic enhancement in the yield strength of all heat treatments, the three age-hardened conditions exhibited a more than 2-fold increase relative to the non-aged heat treatment. This suggests that H modifies the dislocation–precipitate interactions, which also manifest themselves through changes in work hardening metrics related to the dislocation storage and recovery rates. In particular, the H-charged peak-aged specimen exhibited a significant increase in initial hardening (dislocation storage) rate relative to the H-charged under-aged specimen. Transmission electron microscopy of these samples revealed the onset of widespread dislocation looping in the H-charged peak-aged sample, in addition to the planar slip bands characteristic of the non-charged condition. This result suggests that hydrogen induces the particle shearing-to-looping transition at smaller particle sizes. Possible mechanistic explanations for this observed behavior are presented.

Acta Materialia

Quantum-mechanical oxidation states of metal ions in the solid-state binary sulfides

Bingyun Ao

Image, graphical abstractThe solid-state metal sulfides have versatile technological and industrial applications; however, a comprehensive understanding of their chemical states remains in lack mainly due to the complicated bonding behavior of sulfur. Herein I conduct the systematic first-principles DFT + U calculations on the solid-state metal (all transition metals and the early five actinide metals Th, Pa, U, Np, Pu) binary sulfides, focusing on quantitative determination of the quantum-mechanical oxidation states (OSqm) of metal ions by counting d or f orbital occupation numbers. The results show the variation of OSqm of a specific metal ion with sulfur stoichiometry and the trend of OSqm of all considered metal ions. The most remarkable aspect is that OSqm in many sulfides are not consistent with formal OS (OSf) assigned by ionic approximation, especially for the sulfides with the highest sulfur composition. After detailed analysis of OSqm in actinide sulfides, I conclude that the relatively weak bonding between metal and sulfur, the relatively strong S-S bonding interaction, and the localization/itinerancy dual nature of d and f electrons can rationally elucidate the deviation of OSqm from OSf. Such quantitative determination of OSqm in the binary sulfides is expected to offer an alternative for the further exploration of more complicated sulfides and the theoretical design of novel sulfides.

Acta Materialia

Weak influence of ferrite growth rate and strong influence of driving force on dispersion of VC interphase precipitation in low carbon steels

Y.-J. Zhang, G. Miyamoto, K. Shinbo, T. Furuhara

Image, graphical abstractDispersion of nano-sized alloy carbides formed by interphase precipitation at migrating ferrite/austenite interphase boundaries is expected to be affected by local conditions at the boundaries, including ferrite growth rate and driving force for precipitation. The effects of these two factors were systematically investigated by changing alloy composition and transformation temperature. Quantitative analyses by using three-dimensional atom probe reveal that VC interphase precipitation becomes higher in number density and smaller in size at lower transformation temperature or with higher V content. The dispersion of VC is also slightly refined by lower Mn or higher Si content, but remains almost unchanged by increasing the C content. Such variations show good correlations with the driving force for its precipitation that finer VC precipitates can be obtained by enlarging the driving force. In contrast, the influence of the ferrite growth rate on the dispersion in most cases is quite small in the range of this study, which can be explained by considering nucleation kinetics of VC at migrating ferrite/austenite interface.

Acta Materialia

Surface-induced reversal of a phase transformation for the synthesis of ε-Fe 2 O 3 nanoparticles with high coercivity

Marin Tadic, Irena Milosevic, Slavko Kralj, Darko Hanzel, Tanja Barudzija, Laurence Motte, Darko Makovec

Image, graphical abstractA metastable ε-polymorph of iron(III) oxide (ε-Fe2O3) is a very attractive material from the technological, engineering and scientific points of view. In comparison with other iron oxides, it is characterized by unusual magnetic properties and a giant coercivity of ∼20 kOe, which is the largest value among metal oxides. The routine method of ε-Fe2O3 formation is based on the thermal annealing of maghemite (γ-Fe2O3) nanoparticles confined in a silica matrix where the ε-Fe2O3 appears as an intermediate phase between the maghemite and an α-polymorph (α-Fe2O3) hematite (γ→ε→α pathway). In this study, it is demonstrated that the ε→α transformation can be reversed when hematite nanoparticles with an anisotropic hollow morphology are annealed above 600 °C. The observed reversal of the phase stability is explained in terms of an increased nanoparticle surface area and surface energy related to the hollow structure. This study demonstrates the applicability of surface-induced phase transformation to stabilize and control ε-Fe2O3 nanostructures with anisotropic shape and high coercivity ∼1600 kA/m that is one of the key properties of functional magnetic materials for information processing and storage. The understanding of ε-Fe2O3 formation mechanism can provide a new viewpoint and guidance for designing metastable polymorphs and applicative properties.

Acta Materialia

The interaction of deformation twins with long-period stacking ordered precipitates in a magnesium alloy subjected to shock loading

Fan Zhang, Yu Ren, Zhiqing Yang, Huhu Su, Zhen Lu, Chengwen Tan, Hailong Peng, Kentaro Watanabe, Bin Li, Matthew R. Barnett, Mingwei Chen

Image, graphical abstractWe report atomic-scale observations on the interaction of {102} deformation twins with 14H long-period stacking ordered (LPSO) phase in a magnesium alloy. It was found that the interaction strongly depends on the thicknesses of LPSO plates as well as the thickness ratios between LPSO plates and twins. We observed three size-dependent structure responses of LPSO to incoming twins: (1) pure shearing of thin LPSO plates in line with the incursive {102} twins; (2) twin-to-dislocation ‘switch’ from the alpha-Mg matrix to LPSO when LPSO/twin thickness ratios are below a critical value of 0.17±0.05; and (3) elastic deformation of LPSO to accommodate the propagation of incoming twin when LPSO/twin thickness ratios are larger than 0.17±0.05. Moreover, the inter-plate spacing of LPSO also influences the propagation modes of twins by controlling nucleation sites of new twins. These size-dependent interactions are accomplished by local structural transition of face-centered cubic units of LPSO during thin plate shearing and formation of gliding dislocations during LPSO deformation and twin blocked. The atomic-scale observations provide fundamental insights into these interaction modes and, hence, the precipitation strengthening mechanisms in Mg alloys under both quasi-static and dynamic loadings.

Acta Materialia

Phase-field study of IMC growth in Sn–Cu/Cu solder joints including elastoplastic effects

A. Durga, P. Wollants, N. Moelans

Graphical abstract for this articleIn this article, we aim to study the problem of the growth of intermetallic phases in solder joints undergoing mechanical deformation, using a phase-field model for multi-phase systems that can treat diffusion, elastic and plastic deformation. A suitable model is formulated and applied to Sn–Cu/Cu lead-free solder joints. The growth of the intermetallic layers during solid-state annealing is simulated for different strain states. We assess the values of stiffness tensors available in literature and perform ab initio calculations to support the selection of reasonable values from literature. We also perform a parametric study with different eigenstrain values and applied strains. We find that there is a significant effect of the considered eigenstrains and applied strains on the growth kinetics of the system and parabolic growth kinetics is followed in cases where the intermetallic layers grow. We thereby establish the importance of strain in the growth of intermetallic layers and the need for more targeted experiments on the role of strain in the reliability of the solder joint.

Acta Materialia

Combinatorial study of thermal stability in ternary nanocrystalline alloys

Sebastian A. Kube, Wenting Xing, Arvind Kalidindi, Sungwoo Sohn, Amit Datye, Dor Amram, Christopher A. Schuh, Jan Schroers

Image, graphical abstractNanocrystalline alloys can be stabilized through selective grain boundary segregation of specific solute element additions. Increasing attention is being paid to ternary and higher order systems, where complex interactions govern segregation. To efficiently study the large composition spaces of such systems, we apply a high-throughput combinatorial technique revealing nanocrystalline stability through composition-grain-size maps. We compare two systems with distinct binary and ternary alloy interactions: In Pt-AuAg both binaries are expected to be stable, whereas in Pt-AuPd the Pt-Pd binary is unstable and Au-induced co-segregation of Pd was previously reported. For ternary Pt-AuAg we find excellent thermal stability throughout. The Pt-AuPd system, by contrast, divides into an unstable regime, where Pd solute dominates and precipitates, and a stable regime, where Au solute dominates and retains Pd in the grain boundary. Overall, by combining current theory and the introduced combinatorial approach, stable multicomponent nanocrystalline composition spaces can be rapidly determined.

Acta Materialia

Influence of WC-Co hard metal microstructure on defect density, initiation and propagation kinetics of fatigue cracks starting at intrinsic and artificial defects under a negative stress ratio

T. Klünsner, T. Lube, C. Gettinger, L. Walch, R. Pippan

Image, graphical abstractThe fracture behavior of WC-Co hard metals depends on the size of material inhomogeneities or defects from which cracks emanate. The size and frequency of these defects is of high significance to the quantitative understanding of the failure behavior of structural components and metalworking tools made of hard metal. Currently, the interdependence of a hard metal's microstructure, its defect density, its crack nucleation and growth kinetics and its observed fatigue behavior is not completely understood. The current work provides information on the defect density, fatigue limits, fatigue crack initiation thresholds and growth kinetics at a cyclic mean stress of zero for various hard metal grades as a function of their microstructure. The average WC grain size of the investigated materials varied from ultrafine to medium; the Co binder content ranged from 9 to 15 wt. %. The distribution of size and density of defects was determined by analytic relations based on Weibull theory applied to strength distributions determined in three-point bending experiments performed under monotonously increasing load. Fatigue limits were derived from stress amplitude-life curves determined in a six-point bending arrangement under a stress ratio R = σmin/ σmax = -1. Crack growth kinetics were determined for the same stress ratio for artificially cracks in eight-point bending, as well as for cracks emanating from intrinsic subsurface material defects in six-point bending. The observed differences in the fatigue behavior are discussed based on the determined defect densities and the influence of ambient air / vacuum conditions on crack initiation and growth.

Acta Materialia

Structural damage and phase stability of Al 0.3 CoCrFeNi high entropy alloy under high temperature ion irradiation

Tengfei Yang, Wei Guo, Jonathan D. Poplawsky, Dongyue Li, Ling Wang, Yao Li, Wangyu Hu, Miguel L. Crespillo, Zhanfeng Yan, Yong Zhang, Yugang Wang, Steven J. Zinkle

Image, graphical abstractAn initially single phase high entropy alloy (HEA) Al0.3CoCrFeNi was irradiated by 3 MeV Au ions to a fluence of 6 × 1015 cm−2 (∼ 31 dpa at damage peak) at four different temperatures ranging from 250 °C to 650 °C. Transmission electron microscopy (TEM) and Atom probe tomography (APT) were employed to study the evolution of structural damage and phase stability with irradiation temperature. Al0.3CoCrFeNi exhibited a similar evolution of irradiation-induced defects with temperature as compared with conventional FCC alloys. At 250 °C and 350 °C, most of the visible irradiation-induced defects were faulted 1/3<111> dislocation loops. As the irradiation temperature increased to 500 °C, perfect 1/2<110> dislocation loops were observed along with the faulted loops. At the highest irradiation temperature 650 °C, only dislocation lines and networks could be observed. Regarding phase stability, the 3 MeV Au irradiation was observed to suppress the precipitation of (Ni, Al)-enriched nano clusters and the L12 ordered structure at irradiation temperatures 250 °C to 500 °C whereas precipitation of the B2 ordered structure was accelerated at 650 °C. This resulted in qualitatively opposite precipitation behavior between the ion irradiated damage region and unirradiated region at 500 °C and 650 °C. The opposite phase stability of the ion-irradiated damage region and unirradiated region at different temperatures is attributed to the competing effects of ballistic dissolution versus irradiation enhanced diffusion on precipitation.

Acta Materialia

Modeling zirconia sintering trajectory for obtaining translucent submicronic ceramics for dental implant applications

Charles Manière, Geuntak Lee, Joanna McKittrick, Shirley Chan, Eugene A. Olevsky

Image, graphical abstractAttaining high densification without grain growth is one of the main objectives of the sintering optimization in ceramic materials. For dental implant applications, achieving this objective has a decisive impact on the mechanical resistance, the duration and the translucency of the implant. To improve these sintering outcomes a long experimental explorative study is generally required. In this work, we developed a combined experimental/modeling approach allowing a rapid identification of the optimal sintering conditions. The determination of the model densification and grain growth kinetic constitutive parameters has been done experimentally. We found that the sintering/grain growth kinetics have a detrimental acceleration above a critical temperature level. The pressure-less sintering model able to predict the sintering stress, powder densification and grain growth has been used for the determination of the optimal sintering trajectory. We utilized the two step sintering method to approach the critical temperature without an undesirable grain growth. We obtained translucent sintered specimens with a very limited grain growth.

Acta Materialia

MIXING ENTHALPIES OF ALLOYS WITH DYNAMICAL INSTABILITY: bcc Ti-V system.

N.V. Skripnyak, A.V. Ponomareva, M.P. Belov, E.A. Syutkin, A.V. Khvan, A.T. Dinsdale, I.A. Abrikosov

Image, graphical abstractEnthalpy of mixing is among the key materials parameters to determine phase stability and phase transformations in solid solutions. The possibility to predict it from first principles in the framework of the density functional theory is one of the corner stones of the modern materials modeling and the future data-driven materials design. Here we have considered body-centered cubic (bcc) Ti-V alloys, a system with high potential for aerospace, automotive biomedical and energy applications, which is known to exhibit the dynamical instability of the crystal lattice for Ti-rich alloys at low temperature. We have calculated the mixing enthalpies ΔH of bcc Ti-V alloys in the whole interval of concentration at high temperature using ab initio molecular dynamics (AIMD) simulations. A comparison with state-of-the-art static calculations at temperature 0K shows drastic difference between the two methods: while AIMD predicts positive values of ΔH in the whole range of concentrations, the static zero-temperature simulations result in negative values of ΔH for Ti-rich alloys. We have measured the mixing enthalpy of bcc Ti-V alloys experimentally at 1073 K using an isoperibol high temperature Tian-Calvet calorimeter and found that the enthalpies are positive, in agreement with our finite temperature AIMD calculations. We attribute the failure of the standard static calculations of ΔH to lattice distortions associated with the dynamical instability of bcc Ti-V alloys at zero temperature and argue that the effect should be generally important in theoretical predictions of thermodynamic properties, especially for systems with dynamical instability.

Acta Materialia

Shock wave characterization of precipitate strengthening of PH 13–8 Mo stainless steel

G. Hillel, L. Meshi, S. Kalabukhov, N. Frage, E.B. Zaretsky

Image, graphical abstractThe shear stresses required for dislocations passage of highly coherent NiAl-based precipitates, formed in commercial PH 13-8 Mo steel after homogenization, quenching and aging for different duration of time at 510°C, were determined in a series of planar impact experiments using samples with different thickness. The experiments revealed two regimes of decay of the elastic precursor waves: a fast one, at the shear stressτgreater than some thresholdτ*, associated with the interaction of moving dislocations with lattice phonons, and a slow one, at τ < τ*, corresponding to the precipitates` cutting with the help of thermal fluctuations. Consequently, the stress τ* can be regarded as the stress which permits the passage of the precipitate by a dislocation without thermal support. Precipitates` geometry and size, determined based on the activation volume at thermally-activated regime, are in a reasonable agreement with precipitates dimensions estimated from High Resolution Transmission Electron Microscopy images.

Acta Materialia

Grain-boundary structure and segregation in Nb 3 Sn coatings on Nb for high-performance superconducting radiofrequency cavity applications

Jaeyel Lee, Zugang Mao, Kai He, Zu Hawn Sung, Tiziana Spina, Sung-Il Baik, Daniel L Hall, Matthias Liepe, David N Seidman, Sam Posen

Image, graphical abstractWe report on atomic-scale analyses of grain boundary (GB) structures and segregation in Nb3Sn coatings on Nb, prepared by the vapor-diffusion process, for superconducting radiofrequency (SRF) cavity applications, utilizing atom-probe tomography, high-resolution scanning transmission electron-microscopy and first-principles calculations. We demonstrate that the chemical composition of Nb3Sn GBs is correlated strongly with the diffusion of Sn and Nb at GBs during the coating process. In a sample coated with a relatively large Sn flux, we observe an interfacial width of Sn segregation at a GB of ∼3 nm, with a maximum concentration of ∼35 at.%. After post-annealing at 1100 °C for 3 h, the Sn segregated at GBs disappears and Nb segregation is observed subsequently at GBs, indicating that Nb diffused into the Nb3Sn GBs from the Nb substrate. It is also demonstrated that the amount of Sn segregation in a Nb3Sn coating can be controlled by: (i) Sn flux; and (ii) the temperatures of the Nb substrates and Sn source, which may affect the overall kinetics including GB diffusion of Sn and Nb. An investigation of the correlation between the chemical compositions of GBs and Nb3Sn SRF cavity performance reveals that the Nb3Sn SRF cavities with the best performance (high-quality factors at high accelerating electric-field gradients) do not exhibit Sn segregation at GBs. Our results suggest that the chemical compositions of GBs in Nb3Sn coatings for SRF cavities can be controlled by GB engineering and can be utilized to optimize fabrication of high-quality Nb3Sn coatings for SRF cavities.

Acta Materialia

Mesoscopic Origin of Ferroelectric-Ferroelectric Transition in BaTiO 3 : Orthorhombic-to-Tetragonal Domain Evolution

Asaf Hershkovitz, Florian Johann, Maya Barzilay, Alon Hendler Avidor, Yachin Ivry

Image, graphical abstractFerroelectric materials are the core of common technologies, such as medical ultrasound, mobile-phone antennae and low-power memory devices. The technological interest in ferroelectrics stems from the existence of switchable mesoscale polarization domains. Hence, understanding the origin of ferroelectric functionality requires realization of the domain dynamics during a ferroelectric transformation. However, domain dynamics characterization at the mesoscale is typically too slow with respect to the abrupt ferroic transition. Using scanning probe microscopy with 15-mK thermal-, and deep-submicron spatial- resolution, we realized the domain dynamics during an orthorhombic-to-tetragonal transition in the seminal ferroelectric BaTiO3. We show that the transition comprises four distinguishable mechanisms. The dominant mechanism is a step-by-step progression of a tetragonal-domain wavefront into the orthorhombic phase. This progression is accompanied by ripple-like surface irregularities. Small island domains that remained orthorhombic diffuse then slowly after the wavefront progression. Finally, the resultant tetragonal domains equilibrate by coalescing in a constant-speed. These observations, which are accompanied by quantitative data, bridge between existing macroscopic and microscopic models regarding the nature of ferroelectric transitions, showing the mesoscale origin of ferroelectricity.

Acta Materialia

Semi-supervised Learning Approaches to Class Assignment in Ambiguous Microstructures

Courtney Kunselman, Vahid Attari, Levi McClenny, Ulisses Braga-Neto, Raymundo Arroyave

Graphical abstract for this articleUncovering links between processing conditions, microstructure, and properties is a central tenet of materials analysis. It is well known that microstructure determines properties, but expressing these structural features in a universal quantitative fashion has proved to be extremely difficult. Recent efforts have focused on training supervised learning algorithms to place microstructure images into predefined classes, but this approach assumes a level of a priori knowledge that may not always be available. In this paper, we expand this idea to the semi-supervised context in which class labels are known with confidence for only a fraction of the microstructures that represent the material system. It is shown that classifiers which perform well on both the high-confidence labeled data and the unlabeled, ambiguous data can be constructed by relying on the labeling consensus of a collection of semi-supervised learning methods. We also demonstrate the use of novel error estimation approaches for unlabeled data to establish robust confidence bounds on the classification performance over the entire microstructure space.

Acta Materialia

Martensite-Enabled Magnetic Flexibility: the Effects of Post-Growth Treatments in Magnetic-Shape-Memory Heusler Thin Films

Milad Takhsha Ghahfarokhi, Francesca Casoli, Simone Fabbrici, Lucia Nasi, Federica Celegato, Ricardo Cabassi, Giovanna Trevisi, Giovanni Bertoni, Davide Calestani, Paola Tiberto, Franca Albertini

Image, graphical abstractMagnetic-shape-memory Heusler thin films have a great potential for new-concept integrated devices, such as microactuators, energy harvesters and solid-state microrefrigerators, thanks to the intimate coupling between structure and magnetism. The control of microstructure in their martensitic phase is crucial for their full exploitation.

Acta Materialia

Explainable Machine Learning Algorithms To Predict Glass Transition Temperature

Edesio Alcobaça, Saulo Martiello Mastelini, Tiago Botari, Bruno Almeida Pimentel, Daniel Roberto Cassar, André Carlos Ponce de Leon Ferreira de Carvalho, Edgar Dutra Zanotto

Graphical abstract for this articleModern technologies demand the development of new glasses with unusual properties. Most of the previous developments occurred by slow, expensive trial-and-error approaches, which have produced a considerable amount of data over the past 100 years. By finding patterns in such types of data, Machine Learning (ML) algorithms can extract useful knowledge, providing important insights into composition-property maps. A key step in glass composition design is to identify their physical-chemical properties, such as the glass transition temperature, Tg. In this paper, we investigate how different ML algorithms can be used to predict the Tg of glasses based on their chemical composition. For such, we used a dataset of 43,240 oxide glass compositions, each one with its assigned Tg. Besides, to assess the predictive performance obtained by ML algorithms, we investigated the possible gains by tuning the hyperparameters of these algorithms. The results show that the best ML algorithm for predicting Tg is the Random Forest (RF). One of the main challenges in this task is the prediction of extreme Tg values. To do this, we assessed the predictive performance of the investigated ML algorithms in three Tg intervals. For extreme Tg values ( ≤  450 K and  ≥  1150 K), the top-performing algorithm was the k-Nearest Neighbours, closely followed by RF. The induced RF model predicted extreme values of Tg with a Relative Deviation (RD) of 3.5% for glasses with high Tg ( ≥  1150 K), and RD of 7.5% for glasses with very low Tg ( ≤  450 K). Finally, we propose a new visual approach to explain what our RF model learned, highlighting the importance of each chemical element to obtain glasses with extreme Tg. This study can be easily expanded to predict other composition–property combinations and can advantageously replace empirical approaches for developing novel glasses with relevant properties and applications.

Acta Materialia

In situ study of vacancy disordering in crystalline phase-change materials under electron beam irradiation

Ting-Ting Jiang, Xu-Dong Wang, Jiang-Jing Wang, Yu-Xing Zhou, Dan-Li Zhang, Lu Lu, Chun-Lin Jia, Matthias Wuttig, Riccardo Mazzarello, Wei Zhang

Image, graphical abstractUnconventionally high amount of atomic vacancies up to more than 10% are known to form in Ge-Sb-Te crystals upon rapid crystallization from the amorphous phase. Upon thermal annealing, an ordering process of these atomic vacancies is observed, triggering a structural transition from the recrystallized rocksalt structure to a stable layered trigonal structure and a transition from insulator to metal. In this work, we demonstrate an opposite vacancy disordering process upon extensive electron beam irradiation, which is accompanied by the reverse transition from the stable trigonal phase to the metastable cubic phase. The combined in situ transmission electron microscopy experiments and density functional theory nudged elastic band calculations reveal three transition stages, including (I) the vacancy diffusion in the trigonal phase, (II) the change in atomic stacking, and (III) the disappearance of vacancy-rich planes. The mechanism of vacancy disordering is attributed to kinetic knock-on collision effects of the high-energy electron beam, which prevail over the heating effects.

Acta Materialia

Chemical environment and magnetic moment effects on point defect formation in CoCrNi-based concentrated solid-solution alloys

Huaqing Guan, Shaosong Huang, Jianhua Ding, Fuyang Tian, Qiu Xu, Jijun Zhao

Image, graphical abstractAtomic investigation of point defects is the basis for exploring the mechanisms underlying the macro performance of materials under irradiation. Owing to their complex local disordered chemical environments and unique site-to-site lattice distortions, there have been few related studies on high-entropy alloys (HEAs). In this work, we applied ab initio calculations to systemically characterize the chemical environment and magnetic moment effects of point defect formation in three equimolar alloys, namely: CoCrNi, CoCrNiFe, and CoCrNiFeMn. These calculations were based on the investigation of a large number of statistical atomic sites. An appropriate method applying similar atomic environments (SAEs) and an efficient approach using Widom-type substitution techniques were employed to achieve results that were reliable. It was found that the vacancy formation energies (VFEs) were conspicuously larger in the CoCrNiFeMn HEA than in the CoCrNi or CoCrNiFe alloys. The local chemical environment—in particular, the number of first-nearest neighbor (1nn) Ni and Cr atoms—is the key factor affecting the VFE, as vacancies were found to prefer Ni-rich and Cr-poor environments. Interstitial defects were found to be primarily dominated by Co and Mn. Finally, the point defect formation energies were found to be negatively correlated with the anti-magnetic moment changes in 1nn atoms. Our results indicate that the low vacancy generation in HEAs is important for their enhanced irradiation resistance and that the local anti-magnetic moments influences of constituent elements on VFEs provide guidance for the design of advanced radiation-resistant HEAs.

Acta Materialia

Structural failure of layered thermoelectric In 4 Se 3-δ semiconductors is dominated by shear slippage

Min Huang, Guodong Li, Qi An, Pengcheng Zhai, William A. Goddard

Image, graphical abstractIn4Se3-δ semiconductors exhibit high zT as an n-type TE material, making them promising materials for thermoelectric (TE) applications. However, their commercial applications have been limited by the degradation of their mechanical properties upon cyclic thermal loading, making it important to understand their stress response under external loadings. Thus we applied molecular dynamics (MD) simulations using a density functional theory (DFT) derived force field to investigate the stress response and failure mechanism of In4Se3-δ under shear loading as a function of strain rates and temperatures. We considered the most plausible slip system (001)/<100> based on the calculations. We find that shear slippage among In/Se layered structures dominates the shear failure of In4Se3-δ. Particularly, Se vacancies promote disorder of the In atoms in the shear band, which accelerates the shear failure. With increasing temperature, the critical failure strength of In4Se3 and the fracture strain of In4Se3 decrease gradually. In contrast, the fracture strain of In4Se2.75 is improved although the ultimate strength decreases as temperature increases, suggesting that the Se vacancies enhance the ductility at high temperature. In addition, the ultimate strength and the fracture strain for In4Se2.75 increase slightly with the strain rate. This strain rate effect is more significant at low temperature for In4Se2.75 because of the Se vacancies. These findings provide new perspectives of intrinsic failure of In4Se3-δ and theory basis for developing robust In4Se3-δ TE devices.

Acta Materialia

Reactive Modeling of Mo 3 Si Oxidation and Resulting Silica Morphology

Chamila C. Dharmawardhana, Jihan Zhou, Matthew Taylor, Jianwei Miao, John H. Perepezko, Hendrik Heinz

Image, graphical abstractOxidation and corrosion have a significant economic footprint. Mo-based alloys are a strong candidate for structural materials with oxidation resistance at high temperatures. However, understanding of the mechanisms remains limited as experimental techniques do not reach atomic-scale resolution. We examined the mechanism of oxidation of Mo3Si (A15 phase) in Mo-Si-B alloys, the emergence of a superficial silica scale, and explain available experimental data up to the large nanometer scale using chemically detailed reactive simulations. We introduce new simulation protocols for layer-by-layer oxidation and simple force fields for the reactants, intermediates, and products. Growth of thin superficial silica layers as a function of temperature and oxidation rate on the (001) surface involves the formation of silica clusters, rings, and chains with pore sizes of 0 to 2 nm. An increase in temperature from 800 to 1000°C slightly decreased the pore size and lead to less accumulation of Mo oxides at the interface, consistent with observations by electron tomography and energy dispersive X-ray spectroscopy (EDS). The elimination of gaseous MoOx is essential to form open channels and much larger pores up to 100 nm size as observed by 3D tomography, in-situ transmission electron microscopy (TEM) and scanning electron microscopy (SEM) as the oxide phase grows. According to the simulation, these large pores would otherwise be closed. The rate of oxidation, represented by successive oxidation of layers of variable thickness per unit time, influences the structure and cohesion of silica layers. High rates of oxidation can destabilize and break apart the silica layer, supported by a very wide pore size distribution in electron tomography. Limitations of the simulations in time scale currently restrict the analysis to few-layer oxidation. Within these bounds, the proposed simulation protocols can provide insight into the oxidation of (hkl) surfaces, grain boundaries, and various alloys compositions up to the 100 nm scale in atomic-level detail.

Acta Materialia

Facile Healing of Cracks in Organic-Inorganic Halide Perovskite Thin Films

Srinivas K. Yadavalli, Zhenghong Dai, Hua Zhou, Yuanyuan Zhou, Nitin P. Padture

Image, graphical abstractOrganic-inorganic halide perovskite (OIHP) thin films at the heart of the burgeoning thin-film perovskite solar cells (PSCs) technology possess poor mechanical properties, which is likely to limit the long-term reliability of PSCs as they are poised for commercialization. In an effort to address this issue, here we demonstrate that through-thickness cracks induced by bending-tension in thin films of the two prototypical OIHPs, methylammonium lead triiodide (MAPbI3) and formamidinium lead triiodide (FAPbI3), can be healed easily. This is through the application of either a moderate compressive stress (bending-compression) at room temperature or a simple heat-treatment at modest temperatures. The crack-healing process is found to be time-dependent, which indicates that facile mass-transport in OIHPs plays a key role in this phenomenon. An explanation for this phenomenon is provided, one based on the fundamentals of brittle fracture. This discovery has broad implications for the prevention and/or restoration of the overall performance, environmental stability, and mechanical reliability of PSCs, and other devices.

Acta Materialia

Suppression of Shear Localization in Nanocrystalline Al-Ni-Ce Via Segregation Engineering

Glenn H. Balbus, Fulin Wang, Daniel S. Gianola

Graphical abstract for this articleShear localization in nanocrystalline metals is a severely limiting factor precluding their use as practical engineering materials. While several strategies exist to enhance the thermal and mechanical behavior of these materials, there are still many outstanding questions regarding the effects of chemical segregation on shear localization of FCC nanocrystalline materials. In this paper we investigate the mechanical response of a ternary aluminum alloy with a sub-10 nm nanocrystalline microstructure subject to various thermal treatments. Contrary to previous observations, our results suggest that annealing up to 0.7 Tm reduces the propensity for shear localization and increases strength, as demonstrated by a transition in deformation morphology from pronounced strain localization to more homogeneous deformation during indentation. This behavior coincides with the formation of an amorphous intergranular film during annealing, causing intragranular dislocation plasticity to be favored over other grain boundary dominated deformation mechanisms, in turn resulting in a lower propensity for long range plastic localization.

Acta Materialia

Origins of strengthening and failure in twinned Au nanowires: Insights from i n − s i t u experiments and atomistic simulations

Zhuocheng Xie, Jungho Shin, Jakob Renner, Aruna Prakash, Daniel S. Gianola, Erik Bitzek

Graphical abstract for this articleThe deformation behavior of ⟨110⟩-oriented twinned Au nanowires (NWs) with multiple longitudinal coherent twin boundaries (CTBs) under tension is studied using in−situ experiments and molecular dynamics (MD) simulations. The twinned NWs show higher yield strength than the single-crystalline NWs with similar diameter. Postmortem observations using electron microscopy and MD simulations show that the presence of CTBs transitions the governing mechanism from twinning-mediated deformation in single-crystalline NWs to strongly localized deformation. MD simulations reveal that the intersection of deposited partial dislocations at the CTB with the free surfaces plays an important role in the transmission of the dislocation, leading to the formation of full dislocations instead of partial dislocations and twinning in the case of single-crystalline NWs. The repeated activation of full dislocation slip leading to localized deformation is furthermore dependent on the relative orientation of surface facets to the activated Burgers vectors. The results of this work enhance the understanding of deformation mechanisms of twinned nano-objects and suggest design strategies for mechanical systems at the nanoscale.

Acta Materialia

A Model of Grain Boundary Complexion Transitions and Grain Growth in Yttria-Doped Alumina

Philp E. Goins, William E. Frazier

Image, graphical abstractIn this work, we present a physically-parameterized microstructure evolution model for the Yttria-doped alumina system. Yttria-doped alumina is a well-known ceramic system which undergoes first-order phase-like transitions at grain boundaries, which can radically alter interface properties. The change in interfacial properties in turn can radically change microstructure outcomes during processing, including the induction of abnormal grain growth modes. In this work, we develop a simulation that evolves alumina microstructure as a function of yttria concentration and temperature. In the window studied, we achieve strong agreement with reviewed experimental results in identifying the windows for large grains, small grains, abnormal grain growth, and complexion transition kinetics (as measured by JMAK analysis). We then apply the model to study and demonstrate how the possible inclusion of second-phase particles or uneven solute distribution profiles will impact microstructure evolution. It is found that particles do not significantly affect abnormal grain growth in the window studied (but do lead to reduced grain size through pinning effects). It is found that even modest amounts of solute inhomogeneity will result in substantial changes in microstructure outcomes, frequently leading to clusters of abnormal grains. This model largely corroborates the expectations and hypotheses made from recent experimental studies in oxide-doped alumina systems. Further, it is found that there exists a peak transition fraction for the system at which abnormal grain size tends to be maximized.

Acta Materialia

Development of a segregation model beyond McLean based on atomistic simulations

T. Krauß, S.M. Eich

Graphical abstract for this articleIn the present atomistic study, layer-specific segregation to the surface is investigated for an exemplary (100) surface in iron–chromium alloys using an embedded-atom potential. Through a continuous variation of the chemical potential difference in the semi-grandcanonical ensemble, the full composition range is explored at temperatures between 600 K to 1400 K. The obtained layer-specific segregation curves demonstrate the well-known limitations of the widely used McLean model for interface segregation, i.e. a monolayer model imposing ideal behavior. However, keeping the original idea of McLean, the segregation model is extended in two ways in order to provide a complete analytical description of segregation: Firstly, the entire surface is hypothetically replaced by an equivalent single layer with identical segregation properties, which accounts for all subsurface layer effects, but also enables the application of an effective monolayer model with only one single energy of segregation. Secondly, directly following from the general treatment assuming non-ideal solution behavior, the energy of segregation becomes composition-dependent. The validity and accuracy of the proposed analytical model is confirmed by fitting the composition-dependent energy of segregation to the thermodynamically unambiguous solute excess. The change in surface formation energy according to the interfacial adsorption equation can be described excellently over the entire composition range for all investigated temperatures. The model can be applied to experimental data and directly transferred to grain boundaries.

Acta Materialia

Topological and Subsystem Codes on Low-Degree Graphs with Flag Qubits

Christopher Chamberland, Guanyu Zhu, Theodore J. Yoder, Jared B. Hertzberg, and Andrew W. Cross

A new proposed family of quantum error correcting codes and a scalable and efficient flag-based decoding scheme are suitable for implementation in superconducting qubit architectures and offer competitive performance to other error-correction schemes.

Physical Review X

Generalization of Fourier’s Law into Viscous Heat Equations

Michele Simoncelli, Nicola Marzari, and Andrea Cepellotti

Two novel differential equations for heat conduction in crystals generalize Fourier’s law and explain why heat propagation can become fluidlike, rather than diffusive, in electronic or phononic devices.

Physical Review X

Nonlinear Dynamics of Human Aortas for Material Characterization

Marco Amabili, Prabakaran Balasubramanian, Isabella Bozzo, Ivan D. Breslavsky, Giovanni Ferrari, Giulio Franchini, Francesco Giovanniello, and Chloé Pogue

Younger aortas can expand 5 times more than older ones as fluid pumps through them, a finding that could help to design more successful aortic prostheses.

Physical Review X

Quantum-Assisted Measurement of Atomic Diamagnetism

Yaakov Y. Fein, Armin Shayeghi, Lukas Mairhofer, Filip Kiałka, Philipp Rieser, Philipp Geyer, Stefan Gerlich, and Markus Arndt

An atom interferometer reaches a high enough sensitivity to measure the ground-state diamagnetism of single atoms.

Physical Review X

Solving the ${\mathrm{CH}}_{4}^{−}$ Riddle: The Fundamental Role of Spin to Explain Metastable Anionic Methane

Alejandro Ramírez-Solís, Jacques Vigué, Guillermo Hinojosa, and Humberto Saint-Martin

Several types of experiments showed the existence of negative methane ions ${\mathrm{CH}}_{4}^{−}$ over a period of 50 years but the nature of this elusive species remains unknown. A benchmark study has shown that the experimentally observed species cannot be described by the attachment of an electr...

Physical Review Letters

Visualizing Anisotropic Oxygen Diffusion in Ceria under Activated Conditions

Liang Zhu, Xin Jin, Yu-Yang Zhang, Shixuan Du, Lei Liu, Tijana Rajh, Zhi Xu, Wenlong Wang, Xuedong Bai, Jianguo Wen, and Lifen Wang

Oxygen reactivity plays a key role in the performance of ceria-based catalysts. Aberration-corrected transmission electron microscopy and molecular dynamics simulations were used to study the oxygen atom diffusion in ceria under activated conditions. Reactive oxygen atom and its real-time diffusion ...

Physical Review Letters

Critical Transport and Vortex Dynamics in a Thin Atomic Josephson Junction

K. Xhani, E. Neri, L. Galantucci, F. Scazza, A. Burchianti, K.-L. Lee, C. F. Barenghi, A. Trombettoni, M. Inguscio, M. Zaccanti, G. Roati, and N. P. Proukakis

We study the onset of dissipation in an atomic Josephson junction between Fermi superfluids in the molecular Bose-Einstein condensation limit of strong attraction. Our simulations identify the critical population imbalance and the maximum Josephson current delimiting dissipationless and dissipative ...

Physical Review Letters

Rotating a Supersolid Dipolar Gas

S. M. Roccuzzo, A. Gallemí, A. Recati, and S. Stringari

Distinctive features of supersolids show up in their rotational properties. We calculate the moment of inertia of a harmonically trapped dipolar Bose-Einstein condensed gas as a function of the tunable scattering length parameter, providing the transition from the (fully) superfluid to the supersoli...

Physical Review Letters

Full Electrostatic Control of Nanomechanical Buckling

Selcuk Oguz Erbil, Utku Hatipoglu, Cenk Yanik, Mahyar Ghavami, Atakan B. Ari, Mert Yuksel, and M. Selim Hanay

An electromechanical device allows researchers to control and study how a nanoscale beam buckles when compressed.

Physical Review Letters

Curvature Corrections Remove the Inconsistencies of Binary Classical Nucleation Theory

Ailo Aasen, David Reguera, and Øivind Wilhelmsen

The study of nucleation in fluid mixtures exposes challenges beyond those of pure systems. A striking example is homogeneous condensation in highly surface-active water-alcohol mixtures, where classical nucleation theory yields an unphysical, negative number of water molecules in the critical embryo...

Physical Review Letters

General Nanomolding of Ordered Phases

Naijia Liu, Yujun Xie, Guannan Liu, Sungwoo Sohn, Arindam Raj, Guoxing Han, Bozhao Wu, Judy J. Cha, Ze Liu, and Jan Schroers

Large-scale, controlled fabrication of ordered phases is challenging at the nanoscale, yet highly demanded as their well-ordered structure and chemistry is the key for advanced functionality. Here, we demonstrate a general nanomolding process of ordered phases based on atomic diffusion. Resulting na...

Physical Review Letters

Stability of Vicinal Surfaces: Beyond the Quasistatic Approximation

L. Guin, M. E. Jabbour, L. Shaabani-Ardali, L. Benoit-Maréchal, and N. Triantafyllidis

We revisit the step bunching instability without recourse to the quasistatic approximation and show that the stability diagrams are significantly altered, even in the low-deposition regime where it was thought sufficient. In particular, steps are unstable against bunching for attachment-detachment l...

Physical Review Letters

Strain-tuned properties of hybrid improper ferroelectric superlattices through first-principles calculations and machine learning

Monirul Shaikh, Madhusudan Karmakar, and Saurabh Ghosh

The hybrid improper ferroelectricity is due to the trilinear coupling between three symmetric phonon modes, and the free energy of the system can be described as ${F}_{\mathrm{tri}}∼ α\phantom{\rule{4pt}{0ex}}{Q}_{1}{Q}_{2}{Q}_{P}$, where $α$ is the coupling constant and ${Q}_{1}$ and ${Q}_{2}$ are ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Navigating the landscape of nonlinear mechanical metamaterials for advanced programmability

Eder Medina, Patrick E. Farrell, Katia Bertoldi, and Chris H. Rycroft

We consider a flexible mechanical metamaterial comprising an elastomeric matrix with an embedded square array of circular holes. First, we use the deflated continuation technique of bifurcation analysis to explore its complex energy landscape, characterized by multiple bifurcations from which stable...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Probing the local electronic structure of isovalent Bi atoms in InP

C. M. Krammel, A. R. da Cruz, M. E. Flatté, M. Roy, P. A. Maksym, L. Y. Zhang, K. Wang, Y. Y. Li, S. M. Wang, and P. M. Koenraad

Cross-sectional scanning tunneling microscopy (X-STM) is used to experimentally study the influence of isovalent Bi atoms on the electronic structure of InP. We map the spatial pattern of the Bi impurity state, which originates from Bi atoms down to the sixth layer below the surface, in topographic,...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

High-temperature magnetism and crystallography of a ${\mathrm{YCrO}}_{3}$ single crystal

Yinghao Zhu, Si Wu, Bao Tu, Shangjian Jin, Ashfia Huq, Jörg Persson, Haoshi Gao, Defang Ouyang, Zhubing He, Dao-Xin Yao, Zikang Tang, and Hai-Feng Li

Magnetization measurements and time-of-flight neutron powder-diffraction studies on the high-temperature (300–980 K) magnetism and crystal structure (321–1200 K) of a pulverized ${\mathrm{YCrO}}_{3}$ single crystal have been performed. Temperature-dependent inverse magnetic susceptibility coincides ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Atomistic structural mechanism for the glass transition: Entropic contribution

Dong Han, Dan Wei, Jie Yang, Hui-Ling Li, Min-Qiang Jiang, Yun-Jiang Wang, Lan-Hong Dai, and Alessio Zaccone

A popular Adam-Gibbs scenario has suggested that the excess entropy of glass and liquid over crystal dominates the dynamical arrest at the glass transition with exclusive contribution from configurational entropy over vibrational entropy. However, an intuitive structural rationale for the emergence ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Geometric confinement governs toughness and strength in defective diamond nanowires

Zhaocheng Zhang and Zubaer M. Hossain

Using classical molecular dynamics simulations and the virial description of atomic stress, this paper reveals that effective toughness and strength in defective diamond nanowires (NWs) are governed by the geometric confinement of atoms at the critical sites of the NWs. Results suggest existence of ...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Prediction of superconductivity in pressure-induced new silicon boride phases

Xiaowei Liang, Aitor Bergara, Yu Xie, Linyan Wang, Rongxin Sun, Yufei Gao, Xiang-Feng Zhou, Bo Xu, Julong He, Dongli Yu, Guoying Gao, and Yongjun Tian

The crystal structures and properties of boron-silicon (B-Si) compounds under pressure have been systematically explored using particle swarm optimization structure prediction method in combination with first-principles calculations. Three new stoichiometries, ${\mathrm{B}}_{2}\mathrm{Si}$, BSi, and...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Orbital molecules in vanadium oxide spinels

Alexander J. Browne and J. Paul Attfield

X-ray scattering and magnetization measurements have been used to explore the extent of orbital molecule formation in a variety of $A{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ vanadium oxide spinels. Zn doping suppresses the long-range order of trimer-tetramer pairs that occurs in $\mathrm{Ga}{\mathrm{V}}_{2...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Diversity of hole-trap centers due to small polarons and bipolarons in Ca-doped $\mathrm{BiFe}{\mathrm{O}}_{3}$: Origin of electrochromism

Jounghee Lee, Ho-Hyun Nahm, and Yong-Hyun Kim

It has long been controversial whether or not electrochromism with the color change due to applied voltage is caused by small polarons. Recently, the coloration efficiency of Ca-doped $\mathrm{BiFe}{\mathrm{O}}_{3}$ (CBFO) was reported to be more prominent over a wider energy range than that of a co...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Understanding the origin of the magnetocaloric effects in substitutional $\text{Ni-Mn-Sb-}Z(Z=\mathrm{Fe},\mathrm{Co},\mathrm{Cu})$ compounds: Insights from first-principles calculations

Sheuly Ghosh and Subhradip Ghosh

Ni-Mn based ternary Heusler compounds have drawn attention lately as significant magnetocaloric effects in some of them have been observed. Substitution of Ni and Mn by other $3d$-transition metals in controlled quantity has turned out to be successful in enhancing the effect and bring the operation...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Direct observation of the hcp-bcc phase transition and melting along the principal Hugoniot of Mg

M. T. Beason, A. Mandal, and B. J. Jensen

Time-resolved x-ray diffraction was used to examine the phase evolution of polycrystalline Mg shocked along the principal Hugoniot to states that span multiple phase boundaries into the liquid. The diffraction data indicate that the hcp-bcc phase boundary lies above 27 GPa, with the hcp-bcc transiti...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Universality and origin of ultrashort intrinsic negative dielectric permittivity

Sergey Prosandeev, Charles Paillard, B. Xu, and L. Bellaiche

By recasting the definition of the dielectric constants in terms of currents, as well as using atomistic simulations and analytical derivations, we show that the dielectric permittivity can be negative at an ultrashort timescale, under perfect screening conditions and for very different materials an...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Origin of Rashba-Dresselhaus effect in the ferroelectric nitride perovskite ${\mathrm{LaWN}}_{3}$

Subhadeep Bandyopadhyay, Atanu Paul, and I. Dasgupta

First-principles electronic-structure calculations have been employed to investigate the Rashba-Dresselhaus spin splitting of bands in the recently predicted ferroelectric nitride perovskite ${\mathrm{LaWN}}_{3}$. Our first-principles results are supplemented with an effective $\mathbf{k}·\mathbf{p}...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Finite-size corrections for defect-involving vertical transitions in supercell calculations

Tomoya Gake, Yu Kumagai, Christoph Freysoldt, and Fumiyasu Oba

A correction method for vertical transition levels (VTLs) involving defect states calculated with a supercell technique is formulated and its effectiveness is systematically verified with ten defects in prototypical materials: cubic-BN, GaN, MgO, and 3C-SiC. Without any corrections, the absolute err...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Electron polarons and donor point defects in americium dioxide ${\mathrm{AmO}}_{2}$

Martin S. Talla Noutack, Michel Freyss, Gérald Jomard, and Grégory Geneste

Intrinsic donor point defects and electron polarons are investigated in bulk ${\mathrm{AmO}}_{2}$ using density functional theory $+U$ calculations. Oxygen vacancies are deep double-donor defects, with transition energy levels closer to the valence band maximum than to the conduction band minimum. A...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

AtomicNet: a novel approach to identify the crystal structure of each simulated atom

Yuexing Han, Leilei Song, Bing Wang, Sheng Sun, Quan Qian and Qian Wang

The study of crystal structure in the process of plastic deformation is essential to analyse the properties of materials and help to understand the deformation mechanism. With the rapid development of computer hardware and algorithms, great efforts have been paid for atomic simulation with computer science. However, most existing methods can only identify known structures in advance and consider unknown structure as unrecognized ones. In this work, we propose a method to identify crystal structure among atomistic simulations of crystalline materials. First, we develop a new characterization to describe each atom’s local space information, i.e. local spatial characteristics and utilize mutual information to simplify the characteristics. Then, the multi-layer perceptron neural network is used for the classification on the simplified characteristics. With the proposed method, we can not only identify the crystal structures of the surface of atoms, but also obtain the value of proba...

Modelling and Simulation in Materials Science and Engineering

Carbide effects on tensile deformation behavior of [001] symmetric tilt grain boundaries in bcc Fe

Kaimeng Wang, Hongyang Jing, Lianyong Xu, Yongdian Han, Lei Zhao, Wangyu Hu and Huiqiu Deng

The mechanical performance of carbides on the grain boundary (GB) of ferritic steels is always concerned. In this paper, four symmetric tilt GBs in body-centered cubic Fe were studied under tensile tests at 0 and 300 K through atomistic simulations. The GBs contained various sized Cr 23 C 6 precipitates. Stress–strain curves were obtained through the molecular dynamics simulations and the tensile strength varied with GB type. Centro-symmetry parameter, common neighbor and dislocation analyses were performed for defect characterization. GBs with precipitates showed lower tensile strength than pure GBs. As the number and size of carbides increased, the tensile strength decreased. Cavities were easily formed near dislocation loops with a Burgers vector parallel with loading direction during tensile deformation of pure GBs, while ruptures occurred around the precipitate in GBs with carbides. The simulations indicate that Cr 23 C 6 carbides in Fe...

Modelling and Simulation in Materials Science and Engineering

An experimental and theoretical investigation of thermo-mechanical issues in friction surfacing of Al–Mg aluminum alloys: material flow and residual stress

Seyedeh Marjan Bararpour, Hamed Jamshidi Aval and Roohollah Jamaati

Material flow and residual stress distribution during friction surfacing of aluminum alloy AA5083 on aluminum alloy AA5052 substrate have been evaluated employing a three-dimensional model and the finite element software, ABAQUS, as well as experimental investigation. Based on the results, the nature of residual stress in the coating was tensile while getting compressive by straying away from the boundary of the coating. An increment in heat input per unit length of coating has caused a decrease in the maximum tensile residual stress albeit increasing the extent of the region with tensile residual stress. On the advancing side, the velocity vector was larger than the retreating side due to the larger velocity difference between rotating rod and substrate. Moreover, the velocity difference between advancing and retreating sides was much lower in sample with minimum heat input compared to a sample with maximum heat input.

Modelling and Simulation in Materials Science and Engineering

A novel structure-property relationship model based on machine learning

Huiran Zhang, Zhiting Guo, Hongqing Hu, Gaofeng Zhou, Qing Liu, Yan Xu, Quan Qian and Dongbo Dai

In materials science, the relationship between the material internal structure and its associated macroscale properties can be used to guide the design of materials. In this study, we constructed an interpretative machine learning (ML) model to capture the structure-property relationship and predict the solid solubility in binary alloy systems. To do this, we used a dataset containing about 1843 binary alloys and corresponding experiment values of solid solubility. We designed a common function to represent the relationship between individual descriptor and solid solubility, and a deep neural network to integrate the multiple functions. The resulting model can correctly predict the solid solubility value than other ML models. What is more, based on this model, it is feasible to analyze the effect of structures on target property.

Modelling and Simulation in Materials Science and Engineering

Molecular dynamics studies on the strength and ductility of symmetric thermally welded joints

Ishu Aggarwal, Saptarshi Paul, Nishant K Sinha and Sumit Basu

Thermal welding is a common joining technique for polymers. In this work we study the effect of various process parameters on the strength and ductility of a symmetric thermally welded joint through molecular dynamics (MD) simulations on carefully prepared and equilibrated macromolecular ensembles. Interdiffusion of mostly chain ends across the interface and formation of entanglements with chains on the other side constitutes the most important mechanism which determines the strength and ductility of the joint. At high temperatures, the entanglement distribution at the interface can become almost indistinguishable from the bulk rather quickly and without motions of the entire chains. The temperature at which the welding is performed and the welding time are the most important process parameters that control the number of entanglements formed across the interface, the interface width, the mechanical properties and mode of failure of the joint. Pressure and quenching rate have mar...

Modelling and Simulation in Materials Science and Engineering

Structure prediction, high pressure effect and properties investigation of superhard B 6 O

J Zagorac, D Jovanović, T Volkov-Husović, B Matović and D Zagorac

Ab initio data mining approach has been used in order to investigate B 6 O system and discover new possible modifications, besides experimentally known R -3 m ( α -B 6 O) structure and theoretically predicted Cmcm ( β -B 6 O) structure. DFT calculations were performed by two different functionals, LDA and PBE. In this work, we focus on the structure, mechanical, and electronic properties of the experimentally known α -B 6 O structure and newly predicted modifications with the B 6 O stoichiometry. Moreover, mechanical properties including elastic constants, bulk, shear and elastic moduli, Poisson’s ratio, Pugh’s criterion, and hardness are given for the investigated modifications of B 6 O. In particular, we have investigated the influence of the high pressure on the electronic and mechanical properties. Results of our study provide more insight in the B 6 O superhard material...

Modelling and Simulation in Materials Science and Engineering

Solute-strengthening in elastically anisotropic fcc alloys

Shankha Nag, Céline Varvenne and William A Curtin

Dislocation motion through a random alloy is impeded by its interactions with the compositional fluctuations intrinsic to the alloy, leading to strengthening. A recent theory predicts the strengthening as a function of the solute-dislocation interaction energies and composition. First-principles calculations of solute/dislocation interaction energies are computationally expensive, motivating simplified models. An elasticity model for the interaction reduces to the pressure field of the dislocation multiplied by the solute misfit volume. Here, the elasticity model is formulated and evaluated for cubic anisotropy in fcc metals, and compared to a previous isotropic model. The prediction using the isotropic model with Voigt-averaged elastic constants is shown to represent the full anisotropic results within a few percent, and so is the recommended approach for studying anisotropic alloys. Application of the elasticity model using accessible experimentally-measured properties and/or ...

Modelling and Simulation in Materials Science and Engineering

Effect of subsurface voids on the nanoindentation of Fe crystals

Juan A Hofer, Carlos J Ruestes, Eduardo M Bringa and Herbert M Urbassek

Subsurface voids may strongly affect the response of materials to nanoindentation. We explore these effects for a bcc single-crystalline Fe sample using molecular dynamics simulation. Deformation occurs mainly by nucleation and propagation of dislocations. As dislocations impinge into the voids, these suffer a reduction in volume, consistent with mass transfer mechanisms. Our results show that voids act as highly efficient absorbers of dislocations, effectively limiting the extension of the plastic zone. Surprisingly, mechanical properties are marginally affected by the presence of voids in the range of sizes and spatial distributions tested, except for voids a few nanometers below the surface. Deformation twinning is observed as a transient effect in some cases; however, for voids close enough to the indentation area, no twinning was found.

Modelling and Simulation in Materials Science and Engineering

Correlating damage progression to fragmentation at high strain rates using molecular dynamics

B D Huddleston, D E Dickel, Neil Williams, Kent Danielson, Y Hammi, A L Bowman, M I Baskes and M F Horstemeyer

We show a correlation between nanoscale void nucleation and the fragment size by employing atomistic simulations that isotropically expand copper with a varying number of uniform grains at various strain rates and temperatures. Damage within the simulation was quantified in terms of the void number density (void nucleation) and void volume. We quantified the fragment size in terms of a length scale parameter defined as the solid volume-per-surface-area. The relationship of the fragment size to the strain rate was compared to existing models and was found to follow a −1/2 power law. At the atomic scale, the void number density is shown to increase with increasing strain rate, increasing temperature, and decreasing grain size. A fundamental relationship between fragmentation and the internal damage structure is suggested by the correlation between the fragment size and the maximum void number density of a −1/3 power law. We can upscale the relationship between void nucleation and ...

Modelling and Simulation in Materials Science and Engineering

A molecular dynamics simulation study of thermal conductivity anisotropy in β -octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine ( β -HMX)

Rezvan Chitsazi, Matthew P Kroonblawd, Andrey Pereverzev and Tommy Sewell

Molecular dynamics (MD) simulations were used to predict the thermal conductivity of β -octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine ( β -HMX) along directions normal to the (011), (110), and (010) crystal planes. These directions were selected based on the measured morphological importance of the corresponding crystal surfaces. A reverse non-equilibrium MD approach was used wherein a constant heat flux is imposed along a prescribed direction and the resulting steady-state temperature gradient determined. The coefficient of thermal conductivity λ is the quotient of heat flux and temperature gradient (i.e. Fourier’s law). Finite-size effects and sensitivity to imposed heat flux were investigated. The results reveal a modest dependence of the conductivity on crystal orientation, significant finite-size effects, and low sensitivity to imposed flux so long as the Fourier’s law analysis is limited to the spatial interval in the simulation cell for which the temp...

Modelling and Simulation in Materials Science and Engineering

January 22 2020

Keeping It Together: Interleaved Kirigami Extension Assembly

Xinyu Wang, Simon D. Guest, and Randall D. Kamien

Drawing inspiration from kirigami, the art of paper folding and cutting, experiments show how to make lightweight, foldable structures that can support thousands of times their own weight.

Physical Review X

Path integral Monte Carlo and density functional molecular dynamics simulations of warm dense ${\mathrm{MgSiO}}_{3}$

Felipe González-Cataldo, François Soubiran, Henry Peterson, and Burkhard Militzer

In order to provide a comprehensive theoretical description of ${\mathrm{MgSiO}}_{3}$ at extreme conditions, we combine results from path integral Monte Carlo and density functional molecular dynamics simulations and generate a consistent equation of state for this material. We consider a wide range...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

January 20 2020

Microstructural evolution and thermal stability of AlCr(Si)N hard coatings revealed by in-situ high-temperature high-energy grazing incidence transmission X-ray diffraction

N. Jöger, M. Meindlhumer, S. Spor, H. Hruby, J. Julin, A. Stark, F. Nahif, J. Keckes, C. Mitterer, R. Daniel

Graphical abstract for this articleAn extensive understanding about the microstructural evolution and thermal stability of the metastable AlCr(Si)N coating system is of considerable importance for applications facing high temperatures, but it is also a challenging task since several superimposed processes simultaneously occur at elevated temperatures. In this work, three AlCr(Si)N coatings with 0 at.%., 2.5 at.% and 5at.% Si were investigated by in-situ high-temperature high-energy grazing incidence transmission X-ray diffraction (HT-HE-GIT-XRD) and complementary differential scanning calorimetry and thermogravimetric analysis measurements combined with conventional ex-situ X-ray diffraction. The results revealed (i) a change in the microstructure from columnar to a fine-grained nano-composite, (ii) a reduced decomposition rate of CrN to Cr2N, also shifted to higher onset temperatures from  ∼ 1000∘C to above  ∼ 1100∘C and (iii) an increase of lattice defects and micro strains resulting in a significant increase of compressive residual strain with increasing Si content. While the Si-containing coatings in the as-deposited state show a lower hardness of 28GPa compared to AlCrN with 32GPa, vacuum annealing at  ∼ 1100∘C led to an increase in hardness to 29GPa for the coatings containing Si and a decrease in hardness to 26GPa for AlCrN. Furthermore, the in-situ HT-HE-GIT-XRD method allowed for simultaneously accessing temperature-dependent variations of the coating microstructure (defect density, grain size), residual strain state and phase stability up to  ∼ 1100∘C. Finally, the results established a deeper understanding about the relationships between the elemental composition of the materials, the resulting microstructure including crystallographic phases and residual strain state, and the coating properties from room temperature up to  ∼ 1100∘C.

Acta Materialia

New insights into high-temperature deformation and phase transformation mechanisms of lamellar structures in high Nb-containing TiAl alloys

Lin Song, Fritz Appel, Li Wang, Michael Oehring, Xingguo Hu, Andreas Stark, Junyang He, Uwe Lorenz, Tiebang Zhang, Junpin Lin, Florian Pyczak

Image, graphical abstractThe paper describes the microstructure evolution by high-temperature compression of a high Nb-containing TiAl alloy. The paper extends a previous publication [L. Song, et al. Intermetallics 109 (2019) 91-96], in which a unique twin-like morphology in the α2 (Ti3Al) phase was reported. However, the origin of these structures could not be clarified without doubt. The present study is focused on phase transformations that in this multiphase alloy can be associated with deformation. Particular attention is paid to local transformations of the α2 phase into O phase or ω-related phases, which, because of structural and chemical similarity of these phases with α2, can easily occur and could mistakenly be considered as a twin structure. The details of the atomic processes involved are elucidated by electron microscopy. Given the large shufflings and the atomic site interchanges required for the operation of this twinning system, it is concluded that twinning of the α2 phase is a diffusive-displacive process. Within the α2 phase, ωo is heterogeneously nucleated. The nucleation sites are defect-rich areas, which are subjected to high local stresses. The study strongly emphasizes the close relationship between high-temperature deformation and phase transformations in multiphase titanium aluminide alloys.

Acta Materialia

Tunable pyroelectricity, depolarization temperature and energy harvesting density in Pb(Lu 0.5 Nb 0.5 )O 3 - x PbTiO 3 ceramics

Xiaoming Yang, Fangping Zhuo, Chenxi Wang, Ying Liu, Zujian Wang, Chao He, Xifa Long

Image, graphical abstractThe ferroelectric to antiferroelectric (FE-AFE) phase boundary design based on orthorhombic AFE phase and tetragonal FE phase is an effective method to develop high-performance pyroelectric materials due to the complete release of large electrical polarization in FE-AFE phase transition. Herein, we report the phase structure evolution in (1-x)Pb(Lu0.5Nb0.5)O3-xPbTiO3 (abbreviated as PLNT100x) ceramic system based on the relationship of tolerance factors versus electronegativity differences. The composition/temperature effects on FE-AFE phase transition behavior, pyroelectricity, depolarization temperature (Td) and energy harvesting performance were investigated systematically. Obviously, PLNT system displays superior pyroelectric characteristics as well as high Td. The maximum pyroelectric peak was 4.50 μC•cm−2•K−1 over a wide temperature range from 28°C to 167°C. In addition, the obtained maximum pyroelectric energy harvesting density was 1.66 J/cm3 which was much higher than the currently reported values, indicating a potential candidate for pyroelectric energy conversion applications. Based on the modified Ginzburg−Landau−Devonshire (GLD) phenomenology, the composition/temperature driven phase transitions were discussed, and the temperature−electric field (T−E) phase diagram was accordance with actual phase diagram based on the experimental data.

Acta Materialia

Interactions between basal dislocations and β 1 ′ precipitates in Mg–4Zn alloy: mechanisms and strengthening

R. Alizadeh, J. LLorca

Image, graphical abstractThe mechanisms of dislocation/precipitate interaction as well as the critical resolved shear stress were determined as a function of temperature in a Mg–4 wt.% Zn alloy by means of micropillar compression tests. It was found that the mechanical properties were independent of the micropillar size when the cross-section was > 3 × 3 µm2. Transmission electron microscopy showed that deformation involved a mixture of dislocation bowing around the precipitates and precipitate shearing. The initial yield strength was compatible with the predictions of the Orowan model for dislocation bowing around the precipitates. Nevertheless, precipitate shearing was dominant afterwards, leading to the formation of slip bands in which the rod precipitates were transformed into globular particles, limiting the strain hardening. The importance of precipitate shearing increased with temperature and was responsible for the reduction in the mechanical properties of the alloy from 23 °C to 100 °C.

Acta Materialia

Cold Sintering of ZnO-PTFE: utilizing polymer phase to promote ceramic anisotropic grain growth

Thomas Herisson de Beauvoir, Kosuke Tsuji, Xuetong Zhao, Jing Guo, Clive Randall

Densification of ZnO-PTFE (polytetrafluoroethylene) composites is permitted by the Cold Sintering Process, having no effect on the stability of both materials. Highly dense samples can be obtained by this technique at extremely low temperatures in just a few minutes. Interestingly, the obtained samples show an anisotropy impacting: crystalline, microstructural and electrical properties. While the Wurztite ZnO crystals show a preferential growth along (00l) direction, microstructure observations show a grain growth along the in-plane (perpendicular to pressure application direction) up to 240%. Electrical conductivity is also influenced and is related to microstructure. In this situation, the addition of PTFE insulating phase allows to increase the conductivity in plane compared to the pure cold sintered ZnO sample. A mechanism is proposed to explain this phenomenon which involves PTFE transient distribution competing with the transient liquid driving densification and grain growth associated with cold sintering. This is further confirmed by the observation of a curvature of microstructure direction while approaching die edges. These observations offer a large variety of designs for further orientation driven properties.

Acta Materialia

Interface-mediated plasticity of nanoscale Al -Al 2 Cu eutectics

Guisen Liu, Shujuan Wang, Amit Misra, Jian Wang

Image, graphical abstractLaser surface re-melted Al-Al2Cu eutectic alloy with α-Al and θ-Al2Cu nanoscale lamellae exhibits high strength and good plasticity at room temperature, implying that the nanoscale θ-Al2Cu lamellae plastically co-deform with α-Al. Microscopy characterization reveal that plastic deformation of θ-Al2Cu lamellae is accommodated by localized shear on unusual slip planes of {121}Al2Cu. Herein, we elucidate interface-mediated deformation mechanisms of nanoscale Al -Al2Cu eutectics and investigate the structure and properties of the {001}Al‖{001}Al2Cu interface using atomistic simulations. Simulation results reveal that the interface is composed of two sets of misfit dislocations with the displacement shift complete vectors as Burgers vectors. We then conduct simple shear simulations to explore shear response and corresponding mechanisms of the Al-Al2Cu interface, and reveal that interfacial shear is accomplished through the gliding of misfit dislocations on the interface. Plasticity of nanoscale θ-Al2Cu lamellae is examined to be associated with localized shears on {121}Al2Cu planes, which are ascribed to the continuity of slip systems across Al-Al2Cu interfaces and accumulated lattice dislocations at interfaces.

Acta Materialia

Remarkable transport properties switching and surface exchange kinetics in epitaxial PrBaMn 2 O 5+δ films

Mingfeng Chen, Xing Xu, Shanyong Bao, Guang-Kun Ren, Yuan-Hua Lin, A.J. Jacobson, Jing Ma, Ce-Wen Nan, Chonglin Chen

Image, graphical abstractDouble perovskite PrBaMn2O5+δ (PBMO), which demonstrates promising application prospect as ceramic anode material for solid oxide fuel cells, was epitaxially grown on (001) LaAlO3 substrate for determining the nature of surface exchange kinetics and oxygen evolution processes. High-temperature X-ray diffraction, X-ray photoelectron spectroscopy, and transport properties measurement indicated that the oxygen vacancy evolution processes are highly dependent upon the interface strain and temperature. Especially, PBMO thin films show reversible redox reactions in the switches between oxygen and hydrogen atmospheres, and the antiphase domain boundary plays a crucial role in the redox processes. Assembled with YSZ electrolyte, the symmetrical cell shows high efficient processes of surface oxygen exchange and virtue of excellent stability, suggest the PBMO a good candidate for solid oxide fuel cells and chemical sensors.

Acta Materialia

Correlation between Grain Boundary Migration and Stress Corrosion Cracking of Alloy 600 in Hydrogenated Steam

L. Volpe, M.G. Burke, F. Scenini

Image, graphical abstractSolution-annealed Alloy 600 samples were tested under active load conditions in a superheated low pressure H2-steam environment over a range of oxidising potentials relevant to Primary Water Stress Corrosion Cracking (PWSCC). Increased SCC susceptibility was observed for potentials the more reducing than the Ni/NiO transition where a deeper Preferential Intergranular Oxidation (PIO) occurred. Advanced microstructural analysis clearly showed that SCC initiated along the grain boundaries that exhibited Diffusion-Induced Grain Boundary Migration (DIGM), as well as enrichments in Al and Ti. Rather than the result of a single dominant mechanism, the initiation of SCC in Ni-base alloys involves the synergistic interactions between DIGM and the formation of Al- and Ti-enriched oxides, promoting PIO that can fracture with applied stress.

Acta Materialia

Thermally stable superhard diborides: An ab initio guided case study for V-W-diboride thin films

V. Moraes, L. Zauner, T. Wojcik, M. Arndt, P. Polcik, H. Riedl, P.H. Mayrhofer

Graphical abstract for this articleRecent investigations on ternary diborides revealed their enormous potential for the use as protective thin films. Within this study we investigate DC magnetron sputtered V1−xWxB2 thin films (with x= 0, 0.05, 0.13, 0.21) concerning their morphology, structure, mechanical properties, and thermal stability. Ab−initio calculations revealed, that while the equilibrium state of VB2 is the AlB2-prototype (α-type), that of WB2 is the W2B5−x-prototype (ω-type). However, when considering the formation of point defects such as vacancies, the preferred structure of WB2 can even be α, while that of VB2 remains with α. This allows for the formation of metastable α-WB2 – and especially ternary α-V1−xWxB2, which are stable with respect to their constituting α-VB2 and α-WB2 phases (as suggested by DFT and vacuum annealing for 1h at 1400∘ C)even without considering point defects – when using physical vapor deposition, as thereby the point defect concentration is typically high. Our results further show that the highest W-containing ternary coating, V0.69W0.21B2 (which is still single-phase α-structured with a hardness of  ∼ 40 GPa combined with low tensile stresses of 0.3 Pa in the as deposited state) exhibits the highest hardness of  ∼ 43 GPa and  ∼ 40 GPa after 1-h-vacuum annealing at 1000 and 1400∘ C, respectively, among all coatings studied. Their indentation modulus ( ∼ 500 GPa) and also their microstructure (single-phase α-structure, pronounced 0001-orientation, column diameter of 14.7 nm) showed no significant changes up to 1000∘ C.

Acta Materialia

Room temperature deformation of 6 H -SiC single crystals investigated by micropillar compression

Kyosuke Kishida, Yasuharu Shinkai, Haruyuki Inui

Image, graphical abstractThe room-temperature plastic deformation behavior of 6H-SiC single crystals has been investigated by uniaxial compression of micropillar specimens as a function of crystal orientation and specimen size. Plastic flow is observed even at room temperature by basal and prism slip, latter of which have never been observed in the bulk. The CRSS values for basal and prism slip are as high as above 5 and 6 GPa at the specimen size of 5 μm, respectively, each of which increases with decreasing specimen size, following an inverse power-law relationship with a relatively small power-law exponent of ∼0.10 and ∼0.21, respectively. The CRSS values for basal slip are not virtually affected by the existence of basal dislocations introduced at 1300°C prior to micropillar compression tests at room temperature. The majority of basal dislocations observed after micropillar compression are perfect (undissociated) screw dislocations, and they are considered to be introduced in the shuffle-set plane during micropillar testing, unlike widely dissociated dislocations introduced in the glide-set plane in the bulk during high-temperature deformation. Prism dislocations are observed also to glide as perfect (undissociated) dislocations and tend to align strongly along their screw orientation. The fracture toughness values are estimated to be 1.37 ± 0.13 and 1.57 ± 0.13 MPa•m1/2 by three-point bend tests for chevron-notched single crystalline specimens with a notch plane being parallel to (0001) and {011¯0} planes, respectively.

Acta Materialia

Plastically deformed La-Fe-Si: microstructural evolution, magnetocaloric effect and anisotropic thermal conductivity

Yi Ouyang, Mingxiao Zhang, Aru Yan, Wen Wang, Francois Guillou, Jian Liu

Image, graphical abstractLa(Fe,Si)13-based alloys are considered to be one of the most promising magnetocaloric materials for solid state cooling. However, the intrinsic brittleness of NaZn13-type functional phase (1:13 phase) obstructs the shaping of La-Fe-Si alloys into desired geometries for the applications in magnetic cooling devices. Here, by exploiting the excellent deformability of α-Fe phase, we propose a near-net shaping method of open die-forging to prepare La-Fe-Si thin plates. This novel approach is demonstrated for the first time to exhibit several advantages including producing full-dense materials, facilitating the phase formation, and maintaining large magnetocaloric effect. The microstructural and texture evolution have been systematically investigated for the pre-deformed and annealed La-Fe-Si alloys. Large magnetic entropy change of 14 J/kg K at 2 T is obtained in the annealed sample and 11 J/kg K for the hydrogenated sample without hydrogen-induced cracking. Furthermore, a unique dual-phase structure consisting of aligned α-Fe phase and non-equiaxial 1:13 grains brings about the significant anisotropic thermal conductivity in cross-plane and in-plane directions for the plastically-deformed plates. This new insight would greatly benefit the design of high efficient magnetic refrigerator with one-way enhanced thermal conduction.

Acta Materialia

Observation of Three-Photon Spontaneous Parametric Down-Conversion in a Superconducting Parametric Cavity

C. W. Sandbo Chang, Carlos Sabín, P. Forn-Díaz, Fernando Quijandría, A. M. Vadiraj, I. Nsanzineza, G. Johansson, and C. M. Wilson

A long-sought three-photon version of spontaneous parametric down-conversion, a common technique for entangled photon generation, lays the groundwork for expanded investigations into novel types of quantum entanglements and quantum computing resources.

Physical Review X

Fractal-like Mechanical Resonators with a Soft-Clamped Fundamental Mode

S. A. Fedorov, A. Beccari, N. J. Engelsen, and T. J. Kippenberg

Self-similar structures occur naturally and have been employed to engineer exotic physical properties. We show that acoustic modes of a fractal-like system of tensioned strings can display increased mechanical quality factors due to the enhancement of dissipation dilution. We describe a realistic re...

Physical Review Letters

Nucleation Theory for Yielding of Nearly Defect-Free Crystals: Understanding Rate Dependent Yield Points

Vikranth Sagar Reddy, Parswa Nath, Jürgen Horbach, Peter Sollich, and Surajit Sengupta

Experiments and simulations show that when an initially defect-free rigid crystal is subjected to deformation at a constant rate, irreversible plastic flow commences at the so-called yield point. The yield point is a weak function of the deformation rate, which is usually expressed as a power law wi...

Physical Review Letters

Determination of the melting curve of gold up to 110 GPa

Gunnar Weck, Vanina Recoules, Jean-Antoine Queyroux, Frédéric Datchi, Johann Bouchet, Sandra Ninet, Gaston Garbarino, Mohamed Mezouar, and Paul Loubeyre

The melting curve of gold has been measured up to 110 GPa using laser-heated diamond anvil cells and synchrotron x-ray diffraction techniques. Accurate pyrometry temperature measurements and a homogeneous heating of the gold sample were achieved by implementing a sample assembly consisting of two bo...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Annealing temperature dependence of optical and structural properties of Cu films

Jiamin Liu, Meng Wang, Hao Jiang, Jianbin Lin, Honggang Gu, Xiuguo Chen, Tielin Shi, and Shiyuan Liu

Annealing temperature dependency of the optical and structural properties of Cu films is carefully studied using multiple means such as spectroscopic ellipsometry, x-ray diffraction, white-light interferometry, atomic force microscopy, scanning electron microscope (SEM), and the four-probe method. A...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Role of V-V dimerization in the insulator-metal transition and optical transmittance of pure and doped ${\mathrm{VO}}_{2}$ thin films

S. S. Majid, S. R. Sahu, A. Ahad, K. Dey, K. Gautam, F. Rahman, P. Behera, U. Deshpande, V. G. Sathe, and D. K. Shukla

An insulator to metal (IMT) transition $({T}_{t}∼341\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ in the ${\mathrm{VO}}_{2}$ accompanies a transition from an infrared (IR) transparent to IR opaque phase. Tailoring of the IMT and associated IR switching behavior can offer potential thermochromic applicati...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Effects of an atomistic modeling approach on predicted mechanical properties of glassy polymers via molecular dynamics

Dylan M Anstine, Alejandro Strachan and Coray M Colina

Glassy polymers are utilized in numerous applications ranging from light-weight structural materials to membranes for industrial gas separation. In this study, we quantify the ability of non-equilibrium molecular dynamics (NEMD) simulations to predict mechanical properties of glassy polymers based on different modeling approaches: force field selection, number of polymer chains in the simulation cell, and polymer builder algorithm. The polymers analyzed in this work are poly(methyl methacrylate) (PMMA), poly(propylene) (PP), and a polymer of intrinsic microporosity (PIM-1). PMMA samples were synthesized in silico using three different methods: continuous configurational biased Monte Carlo, pseudo-self-avoiding random walk, and a generalized simulated polymerization approach. Following the application of a consistent equilibration approach for each PMMA sample, stress–strain data from simulated tensile testing revealed that the choice of polymer builder algorithm or number...

Modelling and Simulation in Materials Science and Engineering

An efficient space-time phase field discretization for ferroelectrics

Le Van Lich, Tinh Quoc Bui, Thanh-Tung Nguyen, Jie Wang, Trong-Giang Nguyen and Van-Hai Dinh

Recent developments of phase field model based on the Ginzburg–Landau theory have provided an unprecedented look at the formation of polarization domain structures and rich phenomena of polarization behaviors in nanoscale ferroelectrics under electrical and mechanical multi-fields. However, the phase field simulations are often computationally expensive. One of the major reasons behind this inefficiency is due to the complex spatio-temporal effects on the dynamical behavior of polarization. In this work, an efficient scheme with error control and adaptive time-stepping is introduced to the phase field model in the context of Ginzburg–Landau theory. The proposed time adaptivity algorithm is based on the discrete maximum norm of the difference in numerical solutions at three consecutive time steps. In addition, the energy stability of the proposed scheme is demonstrated. Several benchmarks of convergence tests are presented to validate the model. The performance of proposed techni...

Modelling and Simulation in Materials Science and Engineering

January 16 2020

Achieving exceptional radiation tolerance with crystalline-amorphous nanocrystalline structure

Miaomiao Jin, Penghui Cao, Michael P. Short

Graphical abstract for this articleNanostructured materials with amorphous intergranular films (AIFs) have demonstrated superior strength and ductility. The radiation tolerance is expected to be high as the large fraction of interfacial volume efficiently sinks radiation-induced defects. Here, we demonstrate how a crystalline-amorphous system (nanocrystalline Cu with Zr-doped AIFs) responds to continuous irradiation with molecular dynamics simulations. We propose a diffusion model that well characterizes the cascade-driven mixing process, and reveal that the spread of Zr distribution scales linearly with the damage level. The exceptional radiation resistance is attributed to that the interfaces are sustainable defect sinks, that Zr mixing into the bulk enhances local defect annihilation due to solute-interstitial dragging, and that Zr impedes radiation-enhanced grain growth by restraining AIFs from migration and maintaining interface stiffness. These findings suggest that AIF-engineered systems hold promise as highly radiation-tolerant materials with strong structural stability and self-healing capability under radiation damage.

Acta Materialia

Pushing the limits of atomistic simulations towards ultra-high temperature: a machine-learning force field for ZrB 2

Yanhui Zhang, Alessandro Lunghi, Stefano Sanvito

Graphical abstract for this articleDetermining thermal and physical quantities across a broad temperature domain, especially up to the ultra-high temperature region, is a formidable theoretical and experimental challenge. At the same time it is essential for understanding the performance of ultra-high temperature ceramic (UHTC) materials. Here we present the development of a machine-learning force field for ZrB2, one of the primary members of the UHTC family with a complex bonding structure. The force field exhibits chemistry accuracy for both energies and forces and can reproduce structural, elastic and phonon properties, including thermal expansion and thermal transport. A thorough comparison with available empirical potentials shows that our force field outperforms the competitors with the merits of high accuracy and great versatility. Most importantly, its effectiveness is extended from room temperature to the ultra-high temperature region (up to  ∼ 2,500 K), where measurements are very difficult, costly and some time impossible. Our work demonstrates that machine-learning force fields (MLFF) can be used for simulations of materials in a harsh environment, where no experimental tools are available, but crucial for a number of engineering applications, such as in aerospace, aviation and nuclear.

Acta Materialia

Interfacial energy as the driving force for diffusion bonding of ceramics

S. Kovacevic, R. Pan, D.P. Sekulic, S.Dj. Mesarovic

Image, graphical abstractDiffusion bonding of ceramics with a metallic interlayer can give a variety of very complex joint microstructures, which are highly influenced by ceramic compositions, the material and thickness of the interlayer, bonding temperature as well as time at the peak bonding temperature. Experiments with a diffusion bonding of ZrC using a Ti interlayer clearly show that under a certain bonding condition, a seamless joint with the total dissolution of the interlayer can be obtained. They also indicate the existence of the critical interlayer thickness, below which the seamless homogeneous joint domain is obtained, and above which the joint does not homogenize. The key process leading to these outcomes is the diffusion of carbon from ZrC into Ti, which, when the critical carbon concentration is reached, initiates the phase transformation of bcc Ti to TiC, while the binary Zr/Ti diffusion is then driven by entropy and results in a seamless Zr(Ti)C joint.

Acta Materialia

Nanopore-induced dielectric and piezoelectric enhancement in PbTiO 3 nanowires

Meng-Jun Zhou, Tiannan Yang, Jian-Jun Wang, Zhaohui Ren, Long-Qing Chen, Ce-Wen Nan

Image, graphical abstractPorous tetragonal PbTiO3 nanowires, synthesized through an intermediate pre-perovskite structure, exhibit distinct behaviors from those of the corresponding bulk PbTiO3. Here we investigate the role of nanopores in the ferroelectric, dielectric, and piezoelectric properties of ferroelectric PbTiO3 nanowires employing phase-field simulations. It is found that the presence of pores gives rise to large enhancements in both dielectric constant and piezoelectric coefficient by ∼50% and 30%, respectively, compared with those of the bulk PbTiO3. It is shown that the smaller the pore size is, the higher the dielectric and piezoelectric responses of the nanowire are. A charge compensation mechanism is proposed to explain the experimentally measured change of oxygen ions concentration at the pore surfaces. The findings provide in-depth insights into modulation of material properties through nanopores.

Acta Materialia

Understanding the chemistry of cation leaching in illite/water interfacial system using reactive molecular dynamics simulations and hydrothermal experiments

Murali Gopal Muraleedharan, Ryan Herz-Thyhsen, Janet C. Dewey, John P. Kaszuba, Adri C.T. van Duin

Image, graphical abstractDespite long standing pursuit, fundamental questions concerning the chemical pathways of leaching of ions in minerals, a phenomenon crucial to energy extraction, hydrometallurgy, metal recovery, and agriculture remain unanswered. Here we use large-scale ReaxFF reactive molecular dynamics (MD) simulations in combination with hydrothermal experiments to understand the chemistry of leaching in illite exposed to aqueous environment. Our simulations show that potassium counterions leach out into the solution much earlier and in higher concentration when compared with aluminum and silicon, which form the structural network of illite. Upon analyzing the chemical pathway from the trajectory of MD simulations, water molecules supply protons near the illite surface that binds with the non-bridging oxygen (NBO) of the Al-O-Si linkage forming an [Al-O-Si]—H transition state that later converts to silanol group upon Al-O bond dissociation. Proton addition also weakens the interlayer K-O bonds, resulting in the diffusion of K+ ions to illite surface, where they combine with the hydroxyl group formed from water dissociation, to form KOH molecules. KOH molecules diffuse out reactively to bulk water via proton exchange mechanism. Furthermore, we also find that continued protonation results in the formation of Al(OH)3 and Si(OH)4 groups predominantly at the surface, which diffuse out into water resulting in the leaching of Al and Si cations. We also estimated the kinetics of surface reactivity from the MD simulations and explored its effectiveness as a surrogate model for leaching kinetics. However, surface reaction kinetics and experimentally measured leaching kinetics seemed to be off by several orders of magnitude. We also analyzed the effects of leaching on structural distortion and found that more than 20% leaching is required for a notable structural distortion in illite crystal.

Acta Materialia

Generation of misfit dislocations in a core-shell nanowire near the edge of prismatic core

A.M. Smirnov, S.A. Krasnitckii, M.Yu. Gutkin

Image, graphical abstractThe misfit strain relaxation via generation of partial and perfect misfit dislocations and their dipoles at the interface in core-shell nanowires with faceted cores is considered. The core has the shape of a long parallelepiped of a square cross-section and placed symmetrically with respect to the cylindrical shell surface. The energy change caused by dislocation generation in such nanowires is calculated. Critical conditions for the onset of such dislocations are calculated and analyzed. The energy barriers for the dislocation generation are defined with respect to different values of the nanowire parameters. The preference of dislocation configuration and generation sites in the nanowire are determined.

Acta Materialia

Thermodynamic and Phase-field Studies of Phase Transitions, Domain Structures, and Switching for Ba(Zr x Ti 1− x )O 3 Solid Solutions

Yu Hui Huang, Jian-Jun Wang, Tian Nan Yang, Xiao Xing Cheng, Bing Liu, Yong Jun Wu, Long-Qing Chen

Image, graphical abstractWhile extensive experimental activities have been carried out to study the phase transitions and ferroelectric properties of BaZrxTi1-xO3 solid solutions, the corresponding theoretical understanding is largely lacking due to the unavailability of thermodynamic potentials for this system. In this work, an eighth-order polynomial of thermodynamic potential for BaZrxTi1-xO3 (x≤0.3) solid solutions is established based on the existing potential coefficients of BaTiO3 and the experimentally measured phase diagram of BaZrxTi1-xO3 solid solutions. It is then employed to predict and understand the domain structures and switching for BaZrxTi1-xO3 (x≤0.3) single crystals using phase-field simulations. The simulated domain structures and switching are consistent with thermodynamic analysis and available experimental measurements, validating the established thermodynamic potential. It is expected that this thermodynamic potential will find wide applications to studying the phase transitions and ferroelectric properties of BaZrxTi1-xO3 (x≤0.3) bulk and nanoscale materials.

Acta Materialia

Electromigration Effect in Fe-Al Diffusion Couples with Field-Assisted Sintering

Haoren Wang, Rui Kou, Tyler Harrington, Kenneth S. Vecchio

Image, graphical abstractThe electromigration effect in spark plasma sintering (SPS) (a.k.a. field assisted sintering) is quantitively analyzed in the Fe-Al diffusion couple system. In SPS, the samples are heated by a high applied voltage and electric current, which can lead to an electromigration effect. Finite element analysis is utilized to determine the voltage applied to the Fe-Al diffusion couple, which is found to be order of magnitudes smaller than the overall system voltage, indicating the electron wind force would be the dominant mechanism for electromigration in SPS. Additionally, the simulation suggests the temperature and current density distribution is uniform across the metallic diffusion couple, which makes quantitative measurement feasible. A mathematic algorithm that allows diffusivity and electromigration coefficients to be solved, is developed for the Fe-Al, where multiple intermetallic phases coexist. At temperatures below aluminum melting, Fe2Al5 is the single intermetallic phases formed in Fe-Al system, for which electromigration is negligible. At temperatures above aluminum melting, FeAl2, FeAl and α-Fe solid solution phases coexist. Among them, the electromigration effect is noticeable in FeAl phase and is significant in the FeAl2 phase. The corresponding electromigration enhancement constants are calculated.

Acta Materialia

Real-Time Observation of Stacking Faults in Gold Shock Compressed to 150 GPa

Surinder M. Sharma, Stefan J. Turneaure, J. M. Winey, P. A. Rigg, N. Sinclair, Xiaoming Wang, Y. Toyoda, and Y. M. Gupta

A new experimental approach reveals, for the first time, the formation of microstructural defects in gold when shock compressed to high pressure, a critical insight to understanding shocked states of materials.

Physical Review X

Conformal Quasicrystals and Holography

Latham Boyle, Madeline Dickens, and Felix Flicker

The boundary of a discrete spacetime is itself a discrete structure now dubbed a conformal quasicrystal, a fundamental new insight into ideas from holography that attempt to reconcile the conflict between general relativity and quantum physics.

Physical Review X

Supersonic Rotation of a Superfluid: A Long-Lived Dynamical Ring

Yanliang Guo, Romain Dubessy, Mathieu de Goër de Herve, Avinash Kumar, Thomas Badr, Aurélien Perrin, Laurent Longchambon, and Hélène Perrin

Researchers rev up a rotating Bose–Einstein condensate to beyond a critical speed, setting the stage for creating a giant superfluid vortex.

Physical Review Letters

Effect of Magnetic Impurities on Superfluid $^{3}\mathrm{He}$

A. M. Zimmerman, M. D. Nguyen, J. W. Scott, and W. P. Halperin

It is known that both magnetic and nonmagnetic impurities suppress unconventional superconductivity. Here we compare their effect on the paradigm unconventional superconductor, superfluid $^{3}\mathrm{He}$, using highly dilute silica aerogel. Switching magnetic to nonmagnetic scattering in the same ...

Physical Review Letters

Efficient and Versatile Model for Vibrational STEM-EELS

Paul M. Zeiger and Ján Rusz

We introduce a novel method for the simulation of the impact scattering in vibrational scanning transmission electron microscopy electron energy loss spectroscopy simulations. The phonon-loss process is modeled by a combination of molecular dynamics and elastic multislice calculations within a modif...

Physical Review Letters

Oxygen-vacancy donor-electron center in ${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ garnet crystals: Electron paramagnetic resonance and dielectric spectroscopy study

V. Laguta, M. Buryi, P. Arhipov, O. Sidletskiy, O. Laguta, M. G. Brik, and M. Nikl

The ${F}^{+}$ center consisting of an electron trapped at an oxygen vacancy (${V}_{\mathrm{O}}$) was investigated in oxygen deficient ${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ (YAG) garnet crystals by electron paramagnetic resonance (EPR) techniques. The measurements were performed in the...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Plastic flow between nanometer-spaced planar defects in nanostructured diamond and boron nitride

S. H. Zhang, D. Legut, T. C. Germann, S. Veprek, H. J. Zhang, and R. F. Zhang

The fundamental mechanisms of strengthening/hardening and toughening that may be modified by various nanometer-spaced planar defects in the ultrahard nanostructured diamond and boron nitride (BN), e.g., nanotwins, stacking faults, and coherent heterophase interfaces, are still far from understood. I...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Giant tunneling electroresistance in two-dimensional ferroelectric tunnel junctions with out-of-plane ferroelectric polarization

Lili Kang, Peng Jiang, Hua Hao, Yanhong Zhou, Xiaohong Zheng, Lei Zhang, and Zhi Zeng

Ferroelectric tunnel junctions (FTJs) have been intensively studied in recent years due to the great potential in nonvolatile memory devices and two-dimensional (2D) FTJs have started to catch attention lately because of their atomic thickness and their significance in miniaturizing FTJ device sizes...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Dislocation density informed eigenstrain based reduced order homogenization modeling: verification and application on a titanium alloy structure subjected to cyclic loading

Yang Liu, Xiang Zhang, Yiguo Zhu, Ping Hu and Caglar Oskay

This manuscript presents a dislocation density informed eigenstrain based reduced order homogenization model (DD-EHM), and its application on a titanium alloy structure subjected to cyclic loading. The eigenstrain based reduced order homogenization (EHM) approach has been extended to account for the presence of HCP (primary α phase) and BCC ( β phase) grains, within which the deformation process is modeled using a dislocation density based crystal plasticity formulation. DD-EHM has been thoroughly verified to assess the accuracy of the reduced order model in capturing local and global behavior compared with direct crystal plasticity finite element method simulations. A structural scale study of titanium alloy Ti-6242S is performed using DD-EHM to quantify and characterize the spatial distribution and evolution of the dislocation pile-ups subjected to cyclic loading. The evolution of pileups at two spatial scales are tracked using a nonlocal parameter based on disloc...

Modelling and Simulation in Materials Science and Engineering

Interoperability architecture for bridging computational tools: application to steel corrosion in concrete

Zahid M Mir, Jesper Friis, Thomas F Hagelien, Ingeborg-Helene Svenum, Inga G Ringdalen, Natalia Konchakova, Mikhail L Zheludkevich and Daniel Höche

A multiscale modelling framework, especially for corrosion modelling, requires not only robust computational tools but also an efficient datacentric architecture for handling information exchange at different modelling scales. Different computational solvers require and produce data in different programming languages and specific formats signifying a strong non-uniformity for an easy nexus with other solvers. This non-uniformity has created a need to focus on intermittent state-of-the-art datacentric software tools which aim to bridge data exchange heterogeneity across diverse set of solvers. Data organization in the form of metadata structures are presented as a standard for a coherent information representation regardless of the diverse nature of data formats specific to a scientific discipline. This fundamental work presents the concept, underlying terminology and working mechanism of a datacentric architecture tool SOFT5 for exchanging and interfacing data-flow between solve...

Modelling and Simulation in Materials Science and Engineering

January 13 2020

Amorphous intergranular films mitigate radiation damage in nanocrystalline Cu-Zr

Jennifer D. Schuler, Charlette M. Grigorian, Christopher M. Barr, Brad L. Boyce, Khalid Hattar, Timothy J. Rupert

Image, graphical abstractNanocrystalline metals are promising radiation tolerant materials due to their large interfacial volume fraction, but irradiation-induced grain growth can eventually degrade any improvement in radiation tolerance. Therefore, methods to limit grain growth and simultaneously improve the radiation tolerance of nanocrystalline metals are needed. Amorphous intergranular films are unique grain boundary structures that are predicted to have improved sink efficiencies due to their increased thickness and amorphous structure, while also improving grain size stability. In this study, ball milled nanocrystalline Cu-Zr alloys are heat treated to either have only ordered grain boundaries or to contain amorphous intergranular films distributed within the grain boundary network, and are then subjected to in situ transmission electron microscopy irradiation and ex situ irradiation. Differences in defect density and grain growth due to grain boundary complexion type are then investigated. When amorphous intergranular films are incorporated within the material, fewer and smaller defect clusters are observed while grain growth is also limited, leading to nanocrystalline alloys with improved radiation tolerance.

Acta Materialia

Mechanistic investigation of a low-alloy Mg–Ca-based extrusion alloy with high strength–ductility synergy

Hucheng Pan, Rui Kang, Jingren Li, Zhuoran Zeng, Hongbo Xie, Qiuyan Huang, Changlin Yang, Yuping Ren, Gaowu Qin

Image, graphical abstractHigh strength–ductility synergy is difficult to achieve in Mg alloys. Although high strength has been achieved through considerable alloying addition and low-temperature extrusion, these techniques result in low ductility (2–5%). In this work, a novel low-alloy Mg–Ca-based alloy that overcomes this strength–ductility trade-off is designed. The alloy has an excellent tensile yield strength (∼425 MPa) and exhibits a reasonably high elongation capacity (∼11%). A microstructure examination reveals that a high density of submicron grains and nano-precipitates provides the alloy high strength, and the leaner alloy additions and higher extrusion temperatures initially improve ductility. As a result, the density of residual dislocations is reduced, and the formation of low-angle grain boundaries (LAGBs) is enhanced. With fewer residue dislocations, it becomes less probable for the newly activated mobile dislocations to be impeded and transformed into an immobile type during the subsequent tensile test. The LAGBs function as potential sites to emit new dislocations, thus enhancing the dislocation–multiplication capability. More importantly, they can induce evident sub-grain refinement hardening and guarantee that the alloy achieves high strength. The findings lead to a controllable Mg alloy design strategy that can simultaneously afford high strength and ductility.

Acta Materialia

Joint investigation of strain partitioning and chemical partitioning in ferrite-containing TRIP-assisted steels

Xiaodong Tan, Dirk Ponge, Wenjun Lu, Yunbo Xu, Huansheng He, Jun Yan, Di Wu, Dierk Raabe

Image, graphical abstractWe applied two types of hot-rolling direct quenching and partitioning (HDQ&P) schemes to a low-C low-Si Al-added steel and obtained two ferrite-containing TRIP-assisted steels with different hard matrix structures, viz, martensite or bainite. Using quasi in-situ tensile tests combined with high-resolution electron back-scattered diffraction (EBSD) and microscopic digital image correlation (µ-DIC) analysis, we quantitatively investigated the TRIP effect and strain partitioning in the two steels and explored the influence of the strain partitioning between the soft and hard matrix structures on the TRIP effect. We also performed an atomic-scale analysis of the carbon partitioning among the different phases using atom probe tomography (APT). The results show that the strain mainly localizes in the ferrite in both types of materials. For the steel with a martensitic hard-matrix, a strong strain contrast exists between ferrite and martensite, with the local strain difference reaching up to about 75% at a global strain of 12.5%. Strain localization bands initiated in the ferrite rarely cross the ferrite/martensite interfaces. The low local strain (2%-10%) in the martensite regions leads to a slight TRIP effect with a transformation ratio of the retained austenite of about 7.5%. However, for the steel with bainitic matrix, the ferrite and bainite undergo more homogeneous strain partitioning, with an average local strain in ferrite and bainite of 15% and 8%, respectively, at a global strain of 12.5%. The strain localization bands originating in the ferrite can cross the ferrite/bainite (F/B) interfaces and increase the local strain in the bainite regions, resulting in an efficient TRIP effect. In that case the transformation ratio of the retained austenite is about 41%. The lower hardness difference between the ferrite and bainite of about 178 HV, compared with that between the ferrite and martensite of about 256 HV, leads to a lower strain contrast at the ferrite/bainite interfaces, thus retarding interfacial fracture. Further microstructure design for TRIP effect optimization should particularly focus on adjusting the strength contrast among the matrix structures and tuning strain partitioning to enhance the local strain partitioning into the retained austenite.

Acta Materialia

Partial Up-Up-Down Order with the Continuously Distributed Order Parameter in the Triangular Antiferromagnet ${\mathrm{TmMgGaO}}_{4}$

Yuesheng Li, Sebastian Bachus, Hao Deng, Wolfgang Schmidt, Henrik Thoma, Vladimir Hutanu, Yoshifumi Tokiwa, Alexander A. Tsirlin, and Philipp Gegenwart

An investigation of the low-temperature magnetism of TmMgGaO4, a recently synthesized “triangular-lattice Ising antiferromagnet,” reveals an unconventional magnetic architecture that might arise in other similar rare-earth magnets.

Physical Review X

Film Thickness of Pb Islands on the Si(111) Surface

Th. Späth, M. Popp, and R. Hoffmann-Vogel

We analyze topographic scanning force microscopy images together with Kelvin probe images obtained on Pb islands and on the wetting layer on Si(111) for variable annealing times. Within the wetting layer we observe negatively charged Si-rich areas. We show evidence that these Si-rich areas result fr...

Physical Review Letters

Thermally Induced Crossover from 2D to 1D Behavior in an Array of Atomic Wires: Silicon Dangling-Bond Solitons in Si(553)-Au

B. Hafke, C. Brand, T. Witte, B. Sothmann, M. Horn-von Hoegen, and S. C. Erwin

The self-assembly of submonolayer amounts of Au on the densely stepped Si(553) surface creates an array of closely spaced “atomic wires” separated by 1.5 nm. At low temperature, charge transfer between the terraces and the row of silicon dangling bonds at the step edges leads to a charge-ordered sta...

Physical Review Letters

Quadrupole arrangements and the ground state of solid hydrogen

Sebastiaan van de Bund and Graeme J. Ackland

The electric quadrupole-quadrupole $({\mathcal{E}}_{qq})$ interaction is believed to play an important role in the broken symmetry transition from phase I to II in solid hydrogen. To evaluate this, we study structures adopted by purely classical quadrupoles using Markov chain Monte Carlo simulations...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Emergence and role of dipolar dislocation patterns in discrete and continuum formulations of plasticity

Péter Dusán Ispánovity, Stefanos Papanikolaou, and István Groma

The plasticity transition, at the yield strength of a crystal, typically signifies the tendency of dislocation defects towards relatively unrestricted motion. An isolated dislocation moves in the slip plane with velocity proportional to the shear stress, while dislocation ensembles move towards sat...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Modeling the vertical growth of van der Waals stacked 2D materials using the diffuse domain method

Zhenlin Guo, Christopher Price, Vivek B Shenoy and John Lowengrub

Vertically-stacked monolayers of graphene and other atomically-thin 2D materials have attracted considerable research interest because of their potential in fabricating materials with specifically-designed properties. Chemical vapor deposition has proved to be an efficient and scalable fabrication method. However, a lack of mechanistic understanding has hampered efforts to control the fabrication process beyond empirical trial-and-error approaches. In this paper, we develop a general multiscale Burton–Cabrera–Frank type model of the vertical growth of 2D materials to predict the necessary growth conditions for vertical versus in-plane (monolayer) growth of arbitrarily-shaped layers. This extends previous work where we developed such a model assuming the layers were fully-faceted (Ye et al 2017 ACS Nano 11 12780–8). To solve the model numerically, we reformulate the system using the phase-field/diffuse domain method that enables the equations to be solved in...

Modelling and Simulation in Materials Science and Engineering

January 10 2020

Deformation mechanisms and strain rate sensitivity of bimodal and ultrafine-grained copper

J. Bach, M. Stoiber, L. Schindler, H.W. Höppel, M. Göken

Image, graphical abstractMaterials with ultrafine grain size in the range from 100 nm to 1 µm exhibit very high strength paired with a satisfactory ductility when compared to their coarse grained (CG) counterparts. Although this typical behavior is already well known, the dominating deformation mechanisms are still controversially discussed in literature. One idea to explain the deformation behavior of ultrafine-grained metals is that deformation is mainly triggered by grain boundary sliding. Another explanation is that deformation in ultrafine-grained materials is controlled by the thermally activated dislocation annihilation of dislocations at grain boundaries. To gain deeper insights to the relevant deformation mechanisms in UFG metals a systematic study was conducted where the deformation behavior of UFG and bimodal copper (consisting of UFG and CG grains) is compared to the behavior of their CG counterparts. The UFG microstructure was obtained by equal channel angular pressing (ECAP). To achieve a bimodal or coarsened microstructure, specimens were annealed at 125°C or, respectively, at 140°C subsequent to the ECAP-process. Mechanical characterization and investigation on the strain-rate sensitivity were done by compression strain-rate jump tests at room-temperatures and elevated temperatures. It turned out clearly that the degree of bimodality determines the dominant deformation mechanism and the strain-rate sensitivity. In the UFG-state thermally activated annihilation of dislocations at the grain boundaries govern the mechanical behavior. For the bimodal microstructure the annihilation of dislocation at the interface of coarsened grains to the surrounding ultrafine-grained matrix dominate the mechanical behavior. For the fully coarsened state plastic deformation is mainly governed by dislocation interaction in the grain interior. In this regime, annihilation at grain boundaries plays only a minor role.

Acta Materialia

Tracing intermediate phases during crystallization in a Ni-Zr metallic glass

S.Y. Liu, Q.P. Cao, X. Mu, T.D. Xu, D. Wang, K. Ståhl, X.D. Wang, D.X. Zhang, C. Kübel, J.Z. Jiang

Image, graphical abstractCrystallization of metallic glasses (MGs) is a complex dynamic process, driven by thermodynamics and limited by kinetics, which often involves in the phase transformation from the metastable amorphous state, via intermediates, to final stable crystalline states. The intermediate structural state remains mysterious at present but very crucial to a deeper understanding of the physics and mechanisms of the crystallization process. Detailed structural characterization of the complicated intermediate crystalline phases using transmission electron microscopy (TEM) provides a unique platform to study such issues. Here, we monitor the evolution of the crystallization process for Ni65Zr35 (at.%) MG ribbon with structural heterogeneities. Direct visualization combined with compositional analysis reveal that the intermediate phase with Zr concentration higher than that of MG consists of the inter-stacked nanometer-sized layers of Ni-rich units (Ni at.% > 67 %) and Ni10Zr7-like units, where the thin Ni-rich single layer gradually disappears with increasing the annealing temperature. Our findings provide insight into the key role of Ni in the structural transition process, improving the understanding of the atomic diffusion-dominated crystallization in MGs.

Acta Materialia

In-situ observation and analysis of solid-state diffusion and liquid migration in a crystal growth system: A segregation-driven diffusion couple

Anton S. Tremsin, Didier Perrodin, Adrian S. Losko, Sven C. Vogel, Takenao Shinohara, Kenichi Oikawa, Gregory A. Bizarri, Edith D. Bourret, Jeffrey H. Peterson, Kerry P. Wang, Jeffrey J. Derby

Graphical abstract for this articleEnergy-resolved neutron imaging is employed for in-situ measurements of dopant transport in a simple experiment performed before the crystal growth of the scintillator BaBrCl:5%Eu via a vertical gradient freeze technique. During a stabilization period preceding growth, we observed the diffusion of Eu from the solid phase into the melt over a period of approximately 4 hours. Comparing the measured centerline concentration profile with a mathematical model for the system, we estimate the solid-state diffusivity of Eu in BaBrCl as D1=1.9×10−10 m2/s and an upper limit for the liquid-phase diffusivity of Eu in the melt as D2*=2.5×10−10 m2/s, at temperatures near the melting point. We compare this experiment, where diffusion is driven by a concentration discontinuity arising from segregation, to the classical diffusion couple technique. Suggestions are offered on how this segregation-driven couple might be improved as a tool for measuring diffusion coefficients, and we draw attention to the great promise of neutron imaging for in-situ measurements of the distribution of elements, with sufficiently high neutron attenuation coefficients, in difficult environments.

Acta Materialia

Phase change memory materials: Rationalizing the dominance of Ge/Sb/Te alloys

R. O. Jones

Rewritable optical storage is dominated by alloys of a small number of elements, overwhelmingly Ge, Sb, and Te. For over 30 years, Ge/Sb/Te alloys in the composition range ${(\mathrm{GeTe})}_{1−x}{({\mathrm{Sb}}_{2}{\mathrm{Te}}_{3})}_{x}\phantom{\rule{0.28em}{0ex}}(0≤x≤1)$ have been the materials o...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Reconfigurable curved metasurface for acoustic cloaking and illusion

Shi-Wang Fan, Sheng-Dong Zhao, Liyun Cao, Yifan Zhu, A-Li Chen, Yan-Feng Wang, Krupali Donda, Yue-Sheng Wang, and Badreddine Assouar

A severe limitation of current acoustic metasurfaces remains in their modest tunability to meet multifrequency requirements and alterable functionalities on demand. Here, a reconfigurable curved acoustic metasurface for acoustic cloaking and illusion is reported. The structure is composed of an arra...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

January 09 2020

Dynamic observation of Joule heating-induced structural and domain transformation in smart shape-memory alloy

Abdul Karim, Chaoshuai Guan, Bin Chen, Yong Li, Junwei Zhang, Liu Zhu, Xia Deng, Yang Hu, Kaiqi Bi, Hongli Li, Yong Peng, Lingwei Li

Image, graphical abstractFerromagnetic shape-memory alloys can realize smart functional sensors and actuators due to their distinctive capabilities of field-induced strain, which have attracted extensive interests. However, their response and transformation kinetics under the stimulus of Joule heating are still lack, which limits their extensive application into electrical-related sensors. In this work, we firstly report the dynamic structural transformation and magnetic domain evolution of smart shape memory alloy induced by Joule heating in-situ TEM with thermoelectric holder by using Ni2MnGa as experimental model. The stimulus of low-power Joule heating induces the reversible structural and magnetic domain transformations of the smart Ni2MnGa shape memory alloy. Whilst, high-power Joule heating induces an irreversible process of structural transformation and magnetic domain evolution. Our work should be significant to expand the smart shape memory alloy into electrical-related applications.

Acta Materialia

On the Observation of Annealing Twins during Simulating β-Grain Refinement in Ti-6Al-4V High Deposition Rate AM with In-Process Deformation

J. Donoghue, A.E. Davis, C.S. Daniel, A. Garner, F. Martina, J. Quinta da Fonseca, P.B. Prangnell

Image, graphical abstractAdditive Manufacture (AM) of Ti-6Al-4V frequently leads to undesirable, coarse, columnar β-grain structures with a strong <100> fibre texture. In Wire-Arc AM (WAAM), it has been found that the application of a low plastic strain, by methods such as inter-pass rolling, can disrupt β columnar growth and produce a refined, equiaxed grain structure that is more randomly orientated. The origin of this desirable effect has been investigated by thermo-mechanical simulation, direct in-situ EBSD observation, as well as by real-time synchrotron X-ray diffraction (SXRD) during rapid heating. These complementary approaches have shown that, when starting with a WAAM microstructure, the grain refinement process produces a unique micro-texture represented by a four-pole motif symmetrically centred on the parent grain {100} orientations. These new β-grain orientations can be reproduced by a double {112}<111> twinning operation, which produces 12 new, unique, β-orientation variants. High-resolution orientation-mapping techniques and in-situ SXRD heating simulations suggest that the prior β does not twin during deformation, but rather the grain refinement and related texture may be caused by annealing twinning during β re-growth on rapid re-heating of the deformed AM microstructure. Although this is the first time such a unique texture has been observed in a deformed and β annealed Ti-6Al-4V material, it was only found to dominate under the unusual conditions that occur in AM of rapid heating – a fine, lightly deformed α transformation microstructure, with a very coarse starting β-grain structure.

Acta Materialia

Sensitivity of twin boundary movement to sample orientation and magnetic field direction in Ni-Mn-Ga

Medha Veligatla, Christian Titsch, Welf-Guntram Drossel, Carlos J. Garcia-Cervera, Peter Müllner

Image, graphical abstractWhen applying a magnetic field parallel or perpendicular to the long edge of a parallelepiped Ni-Mn-Ga stick, twin boundaries move instantaneously or gradually through the sample. We evaluate the sample shape dependence on twin boundary motion with a micromagnetics computational study of magnetic domain structures and their energies. Due to the sample shape, the demagnetization factor varies with the direction of external magnetic field. When the external magnetic field is applied perpendicular to the long edge of the sample, i.e. in the direction in which the demagnetizing field is highest, the magnetic energy intermittently increases when the strength of the applied magnetic field is low. This energy gain hinders the twin boundary motion and results in a gradual switching, i.e. a gradual magnetization reversal as the applied magnetic field is increased. The formation of 180⁰ magnetic domains offsets this effect partially. In contrast, when the applied magnetic field is parallel to the long edge of the sample, i.e. in the direction in which the demagnetizing field is lowest, the energy decreases with each subsequent magnetization domain reversal and the twin boundary moves instantaneously with ongoing switching. The actuation mode with the field parallel to the long sample edge lends itself for on-off actuators whereas the actuation mode with the field perpendicular to the long sample edge lends itself to gradual positioning devices.

Acta Materialia

On the Remarkable Fracture Toughness of 90 to 97W-NiFe Alloys Revealing Powerful New Ductile Phase Toughening Mechanisms

M.E. Alam, G.R. Odette

Image, graphical abstractTungsten is generally too brittle to serve a robust structural function. Here, we explore the fracture toughness of 90 to 97 wt.%W Fe-Ni liquid phase sintered tungsten heavy alloys (WHAs). The room temperature (RT) maximum load fracture toughness (KJm ≈ 69 to 107 MPa√m) of the WHA, containing only 3 to 10 wt.% of a Ni-Fe ductile phase (DP), is ≈ 9 to 13 times higher than KIc typical of monolithic W (≈ 8 MPa√m). All the WHAs show extensive stable crack growth, and increasing blunting line toughness averaging ≈ 170 MPa√m, prior to significant crack extension. In contrast to classical ductile phase toughening, that is primarily due to macrocrack bridging, the WHA toughness increase mainly involves new mechanisms associated with arrest, blunting and bridging of numerous dilatational shielding process zone microcracks in the macrocrack process zone. Tests down to -196°C, to partially emulate irradiation hardening, show decreasing toughness and a transition to elastic fracture at a temperature of -150°C for 90W to -25°C for 97W. However, even at -196°C, the leanest DP 97W WHA KIc is ≈ 3 times that of monolithic W at RT. Possible effects of the small specimen size used in this study are briefly summarized.

Acta Materialia

Strongly correlated and strongly coupled s-wave superconductivity of the high entropy alloy Ta 1/6 Nb 2/6 Hf 1/6 Zr 1/6 Ti 1/6 compound

Gareoung Kim, Min-Ho Lee, Jae Hyun Yun, Soon-Gil Jung, Woongjin Choi, Tae-Soo You, Jong-Soo Rhyee

Image, graphical abstractHigh entropy alloy (HEA) is a random mixture of multiple elements stabilized by high mixing entropy. We synthesized a Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6 bulk HEA compound as a body-centered cubic structure with lattice parameter a = 3.38 Å based on arc melting. From the electronic and magnetic property measurements, we obtained the superconducting properties such as electron-phonon coupling constant λel-ph, electron-phonon potential Vel-ph, density of states at the Fermi level D(EF), superconducting energy gap 2Δ(0)/kBTc, upper-critical field Hc2(0), coherence length ξ, and critical current density Jc. The compound showed a superconducting transition at Tc = 7.85 K. The compound has relatively sizeable specific heat jump (ΔC/γTc), high effective mass of carrier (29 me), and high Kadowaki-Woods ratio (A/γ2, which plays an important role in the heavy Fermi compounds), indicating that it resides within the strongly coupled s-wave superconductor within a dirty limit. Its vortex pinning force is described by the Dew-Huges double exponential pinning model, implying that there are two types of pinning mechanisms. The possible coexistence of strongly correlated behavior in s-wave superconductivity in HEA compounds is noteworthy because many of the strongly correlated superconductors, such as heavy-fermion and high Tc cuprate superconductors, have nodal gap symmetry. The HEA compound suggests exploiting different types of superconductivity with the current strongly correlated superconductors as well as metallic superconductors.

Acta Materialia

Dislocation ↔ twin transmutations during interaction between prismatic slip and { 10 1 ¯ 1 } twin in magnesium

Peng Chen, Jamie Ombogo, Bin Li

Image, graphical abstractVery unusual and interesting interaction between matrix prismatic dislocations and {101¯1} twin boundaries (TBs) in Magnesium (Mg) was observed in atomistic simulations. When the first prismatic dislocation impinged on the TB, the incoming dislocation was transmuted into a thin layer of {112¯1} twin inside the {101¯1} twin. When successive prismatic dislocations on the same slip plane impinged on the same location at the {101¯1} TB, the {112¯1} twin kept growing toward the opposite {101¯1} TB. Eventually, the {112¯1} twin reached the opposite TB and was then transmuted back to prismatic dislocations that exited the {101¯1} twin and glided into the matrix. Hence, the matrix prismatic dislocations temporarily lose their dislocation identity during twin-slip interaction and then resume their dislocation identity after the interaction is complete. The net effect of these interactions is that the matrix prismatic dislocations transmit across the {101¯1} twin. Lattice correspondence analysis for {101¯1} twinning was performed to understand the mechanism of the interactions. The results show that, the prismatic slip plane is exactly the corresponding plane of {112¯1} twinning. Such a correspondence is consistent with the crystallographic calculations based on classical twinning theory.

Acta Materialia

Accelerated design of novel W-free high-strength Co-base superalloys with extremely wide γ/γʹ region by machine learning and CALPHAD methods

Jingjing Ruan, Weiwei Xu, Tao Yang, Jinxin Yu, Shuiyuan Yang, Junhua Luan, Toshihiro Omori, Cuiping Wang, Ryosuke Kainuma, Kiyohito Ishida, Chain Tsuan Liu, Xingjun Liu

Image, graphical abstractSince half a century ago, researchers have continuously focused on developing γʹ-strengthened Co-base superalloys to achieve an increased power and efficiency; these alloys can supposedly operate at higher temperatures than Ni-base superalloys. However, the yielded results have failed to meet the expectations. Herein, we successfully design novel W-free Co-V-Ta-base alloys by employing machine learning algorithm and CALPHAD methods, which exhibit low mass density (8.67-8.86 g/cm3), an extremely wide γ/γʹ region, a high γʹ solvus temperature (up to 1044 °C), and a high strength. The atom probe tomography results show that titanium is an extremely strong γʹ-former; therefore, it is expected to improve the thermodynamic stability of the γʹ phase. Furthermore, besides the very high tensile strength (18.7 GPa) of γʹ phase, indicated by first-principles calculations, the strength of Ti-incorporated alloy is higher than that of γʹ-strengthened Co-base superalloys; especially, the reported strength value is higher than that of the well-known Co-9Al-9W alloy by approximately 322 MPa at 750 °C, which is comparable to that of a few commercial Ni-base superalloys. Therefore, the possibility of the Co-V-Ta-base system being a candidate for developing novel Co-base superalloys is strongly suggested in this study.

Acta Materialia

Critical assessment of the evaluation of thermal desorption spectroscopy data for duplex stainless steels: a combined experimental and numerical approach

L. Claeys, V. Cnockaert, T. Depover, I. De Graeve, K. Verbeken

Image, graphical abstractThe present study evaluates thermal desorption spectroscopy (TDS) data measured for UNS S32205 duplex stainless steel. Variations in the TDS spectra are obtained by electrochemical hydrogen charging for different times and by applying different heating rates for desorption to evaluate the desorption activation energy. Good agreement is found when comparing the experimental TDS curves with the desorption flux based on a numerical diffusion model using a homogeneous average hydrogen diffusion coefficient for the two-phase (ferrite-austenite) duplex microstructure. Trapping cannot be distinguished from the experimental TDS data since hydrogen diffusion in austenite is the rate-determining process during desorption. An average diffusion activation energy of 43.4 kJ/mol is determined from the experiments. Moreover, similar findings are obtained with a finite-element model that includes the heterogeneous hydrogen-related properties of the two phases of this duplex stainless steel.

Acta Materialia

“Self-sharpening” tungsten high-entropy alloy

X.F. Liu, Z.L. Tian, X.F. Zhang, H.H. Chen, T.W. Liu, Y. Chen, Y.J. Wang, L.H. Dai

Image, graphical abstract“Self-sharpening”, a material maintaining its acute head shape during penetration, is highly desirable in a wide range of engineering applications. However, it remains a great challenge to make it occur in conventional single-principal-element alloys. Here, we develop a new chemical-disordered multi-phase tungsten high-entropy alloy that exhibits outstanding self-sharpening capability, in sharp contrast to conventional tungsten alloys only showing mushrooming. This alloy consists of a BCC dendrite phase and a rhombohedral μ phase embedded in the continuous FCC matrix, and such a unique microstructure leads to a 10-20% better penetration performance than conventional tungsten heavy alloys. We show that emergence of the self-sharpening is triggered by the ultrastrong μ phase stimulated dynamic recrystallization softening mediated shear banding. This study sheds light on the origin of self-sharpening and might open new opportunities for developing high-performance penetrator materials.

Acta Materialia

Metal hetero-diffusion along the metal-ceramic interfaces: a case study of Au diffusion along the Ni-sapphire interface

Hagit Barda, Eugen Rabkin

Image, graphical abstractWe propose a new method for determining the hetero-diffusion coefficient of metals along the metal-ceramic interfaces. The samples for diffusion studies are produced by partial dewetting of thin metal film deposited on ceramic substrate, followed by the deposition of an ultrathin layer of a diffuser. The latter covers both the partially dewetted thin film and the dewetting holes exposing the substrate. During diffusion anneal, the diffuser penetrates from the triple lines along the film-substrate interface. We apply this method for studying the diffusion of Au along the Ni-sapphire interface. Our experiments yield the pre-exponential factor and activation energy of 2.217−2.208+535×10−6m2s and 179±33kJmol−1, respectively. Our results demonstrate that in the examined temperature range (450 – 550°C), interface diffusion is slower than grain boundary hetero-diffusion, but faster than bulk diffusion of Au in Ni.

Acta Materialia

Pressureless Two-Step Sintering of Ultrafine-Grained Tungsten

Xingyu Li, Lin Zhang, Yanhao Dong, Rui Gao, Mingli Qin, Xuanhui Qu, Ju Li

Image, graphical abstractThe challenge of producing dense ultrafine-grained (UFG) tungsten is hereby addressed by a simple pressureless two-step sintering method. It provides a uniform microstructure with ∼99% theoretical density and ∼700 nm grain size, which is among the best sintering practice of pure tungsten reported in the literature. Benefitting from the finer and more uniform microstructures, two-step sintered samples show better mechanical properties in bending strength and hardness. While parabolic grain growth kinetics is verified, a transition in the nominal grain boundary mobility was observed at 1400 °C, above which the effective activation enthalpy is ∼6.1 eV, below which grain boundary motion is rapidly frozen with unusually large activation enthalpy of ∼12.9 eV. Such highly nonlinear behavior in activation parameters with respect to temperature suggests that activation entropy and maybe collective behavior play a role. We believe the as-reported two-step sintering method should also be applicable to other refractory metals and alloys, and may be generalized to multi-step or continuous-cooling sintering design using machine learning.

Acta Materialia

Precipitation-induced mitigation of recrystallization in ultra-thin, cold-rolled AlScZrMn(Mg) sheets at brazing temperatures: the critical effect of alloy composition and thermal processing route

Qingshan Dong, Andrew Howells, Mary Gallerneault, Vahid Fallah

Image, graphical abstractUsing advanced electron microscopy techniques, statistical analysis and analytical investigation of precipitates/dispersoids evolution, we demonstrate the critical effect of alloy composition (Sc, Mn, and Mg content) and thermal processing route (heating rate and pre-aging) on the recrystallization behaviour of AlScZrMn(Mg) alloys. Two major types of second phases, namely Al3(Sc,Zr) precipitates and α-Al(Mn,Fe)Si dispersoids, were identified in the thermally-treated cold-rolled sheets (of 0.3 mm thickness). Both phases were observed to maintain coherency with the Al matrix at abnormally large sizes (>100 nm and >500 nm, respectively), as well as exhibiting unprecedented levels of thermal stability (i.e., high coarsening resistance). The recrystallization behaviour and strength evolution were shown to be a strong function of the size and aerial number density evolution of the precipitates/dispersoids which, in turn, are controlled by the alloy composition and thermal history. Particularly, the recrystallization was effectively mitigated at a slow ramp to 590°C (a typical brazing temperature for AlMn alloys) whereas a full recrystallization occurred during a faster ramp. Such behaviour was explained by the competitive kinetics of Al3(Sc,Zr) precipitation and recrystallization phenomenon at intermediate and high-temperature ranges upon heating to 590°C. The introduction of a pre-aging treatment within the intermediate temperature range (i.e., 250-400°C), prior to the fast ramp, was shown to prevent recrystallization due to the stabilization effect of a large aerial number density of finely-dispersed Al3(Sc,Zr) precipitates. A higher Sc content in the alloy enhances such a stabilization effect. Mn additions not only enhance the mitigation of recrystallization (through a refinement of Al3(Sc,Zr) precipitates) but also refines the evolution of α-Al(Mn,Fe)Si dispersoids resulting in a higher yield strength. The Mg addition, on the other hand, has no impact on the evolution of Al3(Sc,Zr) precipitates nor on the recrystallization status, though it causes a refinement of α-Al(Mn,Fe)Si dispersoids and thus leads to a higher final yield strength. The extraordinary high-temperature stability of cold-rolled thin sheets, obtained by the alloy and process design in this study, can be effectively utilized for many light-weight applications of AA3xxx Al alloys.

Acta Materialia

Shuffle-nanodomain regulated strain glass transition in Ti-24Nb-4Zr-8Sn alloy

Qianglong Liang, Dong Wang, Yufeng Zheng, Shuangshuang Zhao, Yipeng Gao, Yulin Hao, Rui Yang, Dipankar Banerjee, Hamish L. Fraser, Yunzhi Wang

Image, graphical abstractThe unprecedented properties of multi-functional metastable β-Ti alloys, including superelasticity over a wide temperature range, ultra-low modulus, and Invar and Elinvar anomalies, have attracted a great deal of attention. Persistent research efforts have been made towards the understanding of the origins of these unique properties. In this article we report a novel shuffle-nanodomain regulated strain glass transition in a metastable β-Ti alloy, Ti-24Nb-4Zr-8Sn (wt.%, Ti2448), which could be the dominant transformation pathway that offers these unique properties. Using the ex-situ aberration-corrected scanning transmission electron microscopy and in-situ cooling transmission electron microscopy, we find that randomly distributed {011}〈01¯1〉β Oʹ phase (orthorhombic, shuffle only) nanodomains embedded in the β (BCC) phase matrix at room temperature transform to α″ phase (orthorhombic) with a continuous increase in the amount of {21¯1}〈1¯1¯1〉β shear upon cooling or loading. Crystallographic analysis shows that the shuffle of the Oʹ phase will restrain the twelve possible shears that transform a BCC lattice to α″ martensite to only two. Thus, the randomly distributed Oʹ nanodomains prevent the formation of long-range-ordered, self-accommodating transformation-strain domain patterns seen in normal martensitic transformations and suppress completely the sharp first-order, auto-catalytic and avalanche-like martensitic transformation into a high-order-like (continuous) strain glass transition. Such a continuous β  →  Oʹ  →  α″ strain glass transition has been confirmed by dynamic mechanical analysis, resistivity and differential scanning calorimetric measurement. This unique transition pathway allows us to offer new insights into the unique properties found in this alloy.

Acta Materialia

From Coherent to Semicoherent–Evolution of Precipitation Crystallography in an fcc/bcc System

Fu-Zhi Dai, Zhi-Peng Sun, Wen-Zheng Zhang

Image, graphical abstractHow are crystallographic features developed in phase transformation systems with anisotropic misfits (e.g., bcc/fcc systems)? Comprehensive knowledge about this question is still very limited, which impedes the thorough understanding and the quantitative modeling of microstructure evolution. In this work, we simulated the early stage growth of a Cr precipitate (bcc) in a Cu matrix (fcc) by combining Monte Carlo and molecular dynamics. The simulation results reveal fine details about the evolution of crystallographic features, including the orientation relationship (OR) between the two phases, the precipitate morphology, and the interfacial dislocation structures. The governing event during the evolution process is the generation of a dominant set of dislocations. The selection of the dominant dislocations is rationalized based on minimization of the interfacial energy in the major facet, which contains a single set of dislocations. The initial OR between the coherent precipitate and the matrix is close to the Nishiyama-Wassermann OR. In response to the generation of the dominant dislocations, the OR jumps towards the ideal OR corresponding to the O-line condition, which is close to the Kurdjumov-Sachs OR. This tendency reflects the experimental observations in a Cu-Cr system and provides helpful insight into the actual evolution of crystallographic features.

Acta Materialia

Comparative Study of Radiation Defects in Ion Irradiated Bulk and Thin-Foil Tungsten

Ruo-Yao Zheng, Wei-Zhong Han

Image, graphical abstractIn this study, we employ transmission electron microscope (TEM) to analyze radiation defects in helium (He) and krypton (Kr) ions implanted bulk and thin-foil tungsten. For bulk tungsten, subgrains are formed near the surface region under both He+ and Kr+ irradiation. Dislocation loops are observed beyond ion implanted range. These observations are related to self-interstitial atoms (SIAs) diffusion and clustering. Ordered bubbles are formed in He+ implantation, while no cavities are detected in Kr+ irradiation. In thin-foil tungsten, line up of dislocation loops is found mainly aligns along {101} and {112} slip planes. Both 1/2<111> and <100> dislocation loops are identified. Compared to He+ irradiation, more <100> loops are detected in Kr+ irradiation due to higher energy collision cascade. Nanocavities are detected in irradiated thin-foil tungsten besides the formation of high density of interstitial loops. The number density of dislocation loops and the volume fractions of cavities are higher in He+ irradiation than in Kr+ irradiation. The differences in nature of radiation defects is attributed to the higher recombination rate of vacancies and interstitials in bulk sample, the significant surface sink effect in thin-foil irradiation and the chemical and physical effect of implanted ions.

Acta Materialia

Dislocation nucleation and evolution at the ferrite-cementite interface under cyclic loadings

Lun-Wei Liang, Yun-Jiang Wang, Yan Chen, Hai-Ying Wang, Lan-Hong Dai

Image, graphical abstractFatigue is of significant importance to the engineering applications of the structural materials. High-strength pearlite steel consisting of a ductile ferrite phase and a brittle cementite phase is a widely used structural metal for extreme load-bearing applications. However, the fatigue mechanisms of such important materials remain elusive, in particular, the atomic-scale dislocation behaviors at interface are poorly understood. We used molecular dynamics simulations to probe the mechanical response and deformation mechanism of the Bagaryatskii-oriented ferrite-cementite interface in pearlite. The interface was subjected to a hundred symmetric tension-compression deformation cycles. Three different loading schemes with strain magnitudes of 4.0%, 6.0%, and 9.0% are sophisticatedly designed to explore the cyclic plastic mechanisms under different conditions corresponding to pure elasticity, elasticity in tension but plasticity in compression, and plasticity in both tension and compression, respectively. During cyclic deformation, rapid dislocation accumulation occurs in the first 30 cycles, after which dislocation density decreases to a stable value in ferrite. It is found that the onset of plasticity is governed by dislocation nucleation from the ferrite-cementite interface. After slip into the ferrite phase, some dislocations annihilate at the interface. After a few tens of cycles, the dislocation nucleation and annihilation rates become equal, leading to a steady-state flow in cyclic deformation. Up to high cycles with large strain magnitude, the magnitude of plastic strain in pearlite is higher than critical values and slip crosses the interface from the ferrite phase to the brittle cementite phase. Dislocation slip in cementite will destroy the interface structure, which may be the plastic mechanism of final fatigue failure. Our simulations agree with experimental observations of dislocation evolution in the ratchetting of pearlite steels and provide further atomic-scale mechanisms to explain the fatigue failure of these materials.

Acta Materialia

An integrated experimental and computational study of diffusion and atomic mobility of the aluminum-magnesium system

Wei Zhong, Mohammad Shahriar Hooshmand, Maryam Ghazisaeidi, Wolfgang Windl, Ji-Cheng Zhao

Image, graphical abstractDiffusion between Al and Mg was investigated comprehensively using both high-throughput experiments and density functional theory (DFT) calculations. Experimental diffusion coefficients in fcc Al, hcp Mg, β–Mg17Al12, γ–Mg2Al3 andε−−Mg23Al30 phases were collected by combining diffusion multiples with forward-simulation analysis together with a critical review of the experimental studies in the literature. The best settings to compute the dilute (impurity) diffusion coefficients of Al and Mg using DFT were tested by comparing the computed data using various DFT settings with the critically assessed experimental diffusion coefficients in stable phases (fcc Al and hcp Mg). The optimal DFT settings were employed to calculate the dilute diffusion coefficients of Al and Mg in metastable (hypothetical) phases (hcp Al and fcc Mg) where experimental measurements were impossible. The atomic mobilities of Al and Mg in the Al-Mg binary system across the entire composition range were then reliably optimized for both the fcc and hcp phases based on the comprehensive diffusion data obtained from both experimental measurements for the stable phases and DFT calculations for the metastable phases. This study demonstrates an efficient and reliable way to develop the fundamental mobility databases using integrated experimental and computational methods.

Acta Materialia

Classical Dimers on Penrose Tilings

Felix Flicker, Steven H. Simon, and S. A. Parameswaran

A new analysis shows that the edges of a Penrose tiling cannot be colored such that every vertex connects to precisely one colored edge, an insight with implications for the study of topological order.

Physical Review X

Rigidity-Controlled Crossover: From Spinodal to Critical Failure

Hudson Borja da Rocha and Lev Truskinovsky

Failure in disordered solids is accompanied by intermittent fluctuations extending over a broad range of scales. The implied scaling has been previously associated with either spinodal or critical points. We use an analytically transparent mean-field model to show that both analogies are relevant ne...

Physical Review Letters

Probing the Solid Phase of Noble Metal Copper at Terapascal Conditions

D. E. Fratanduono, R. F. Smith, S. J. Ali, D. G. Braun, A. Fernandez-Pañella, S. Zhang, R. G. Kraus, F. Coppari, J. M. McNaney, M. C. Marshall, L. E. Kirch, D. C. Swift, M. Millot, J. K. Wicks, and J. H. Eggert

Ramp compression along a low-temperature adiabat offers a unique avenue to explore the physical properties of materials at the highest densities of their solid form, a region inaccessible by single shock compression. Using the National Ignition Facility and OMEGA laser facilities, copper samples wer...

Physical Review Letters

Unveiling dislocation characteristics in $\mathrm{N}{\mathrm{i}}_{3}\mathrm{Al}$ from stacking fault energy and ideal strength: A first-principles study via pure alias shear deformation

Shun-Li Shang, John Shimanek, Shipin Qin, Yi Wang, Allison M. Beese, and Zi-Kui Liu

Nickel aluminide $(\mathrm{N}{\mathrm{i}}_{3}\mathrm{Al})$ is an important material for a number of applications, especially when used as a strengthening constituent in high-temperature Ni-based superalloys. Despite this, there is minimal information on its mechanical properties such as strength, pl...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Dirac degeneracy and elastic topological valley modes induced by local resonant states

Quan Zhang, Yi Chen, Kai Zhang, and Gengkai Hu

In elastic systems, the current technique to produce Dirac degeneracy is based on Bragg scattering eigenstates, which, however, suffers from operating only at relatively high frequency determined by lattice constant. Here, an elastic metamaterial plate that presents an analog to the quantum valley H...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

January 07 2020

Room temperature polar structure and multiferroicity in $\mathrm{BaFe}{}_{2}\mathrm{Se}{}_{3}$

W. Zheng, V. Balédent, M. B. Lepetit, P. Retailleau, E. V. Elslande, C. R. Pasquier, P. Auban-Senzier, A. Forget, D. Colson, and P. Foury-Leylekian

The understanding of the superconducting phase under pressure in the famous iron-based spin ladder ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{3}$ commands a perfect understanding of the structural properties. We present an accurate single crystal x-ray analysis which demonstrates that the structure admitted...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

January 06 2020

Designing rare-earth free permanent magnets in Heusler alloys via interstitial doping

Qiang Gao, Ingo Opahle, Oliver Gutfleisch, Hongbin Zhang

Graphical abstract for this articleBased on high-throughput density functional theory calculations, we investigated the effects of light interstitial H, B, C, and N atoms on the magnetic properties of cubic Heusler alloys, with the aim to design new rare-earth free permanent magnets. It is observed that the interstitial atoms induce significant tetragonal distortions, leading to 32 candidates with large ( >  0.4 MJ/m3) uniaxial magneto-crystalline anisotropy energies (MAEs) and 10 cases with large in-plane MAEs. Detailed analysis following the the perturbation theory and chemical bonding reveals the strong MAE originates from the local crystalline distortions and thus the changes of the chemical bonding around the interstitials. This provides a valuable way to tailor the MAEs to obtain competitive permanent magnets, filling the gap between high performance Sm-Co/Nd-Fe-B and widely used ferrite/AlNiCo materials.

Acta Materialia

Unveiling the pinning behavior of charged domain walls in BiFeO 3 thin films via vacancy defects

W.R. Geng, X.H. Tian, Y.X. Jiang, Y.L. Zhu, Y.L. Tang, Y.J. Wang, M.J. Zou, Y.P. Feng, B. Wu, W.T. Hu, X.L. Ma

Image, graphical abstractManipulation of electronic states in functional ferroelectrics is promising for next generation electronics devices. The charged domain walls in ferroelectric materials especially facilitate the electronic state modulation and are promising for developing interface-based devices. However, the major challenges impeding the application are their intentional manipulation and the elusive pinning behavior. Here, results that charged domain walls in BiFeO3 films can be pinned and regulated by oxygen vacancy planar distributions controlled by oxygen pressure during film growth are reported. Using aberration-corrected scanning transmission electron microscopy complemented by theoretical simulations, rich pinning behavior of tail-to-tail charged domain walls by oxygen vacancy plates is revealed. At high annealing oxygen pressure, 71° charged domain walls are stabilized by narrow vacancy plates. Decreasing the oxygen pressure, the transformation from 71° to 109° charged domain walls happens by expanding the vacancy plates, as collaborated by phase field simulations. Besides, the 71°-109° charged domain wall pairs are stabilized due to further interaction between two neighboring vacancy plates. These results provide the active modulation of the electronic states and illuminate the rich pinning behavior of domain walls by vacancy defects in ferroelectrics, which in turn could provide implications for designing potential electronics devices.

Acta Materialia

Deformation twinning during high temperature compression tests of the Ni-base superalloy ATI 718Plus®

Christiane Kienl, Fernando D. León-Cázares, Catherine M.F. Rae

Graphical abstract for this articleThis study discusses the deformation mechanisms active during high temperature compression tests of the Ni-base superalloy ATI 718Plus®. Deformation twins were observed in deformed grains across a range of temperatures and strain rates by use of transmission electron microscopes (TEM). Even at strain rates as low as 0.01 s−1 and temperatures up to 1025∘C the microstructure contained of grains which deformed by deformation twinning. It was concluded that the low stacking fault energy of the alloy, which was measured to be 15mJm−2 caused the formation of the deformation twins. In addition, several examples of the early stages of twin formation were captured. The twinning partials were in most cases emitted from grain boundaries. In a second instance cross-slip events from a Frank-Read source lead to the formation of partials which formed stacking faults.

Acta Materialia

Spectroscopic Visualization of a Robust Electronic Response of Semiconducting Nanowires to Deposition of Superconducting Islands

Jonathan Reiner, Abhay Kumar Nayak, Amit Tulchinsky, Aviram Steinbok, Tom Koren, Noam Morali, Rajib Batabyal, Jung-Hyun Kang, Nurit Avraham, Yuval Oreg, Hadas Shtrikman, and Haim Beidenkopf

The electronic behavior of indium arsenide nanowires is barely affected by the presence of superconducting aluminum electrodes, an insight that could be useful for designing robust quantum-based technologies.

Physical Review X

Robust Fano resonance in a topological mechanical beam

Wei Wang, Yabin Jin, Wan Wang, Bernard Bonello, Bahram Djafari-Rouhani, and Romain Fleury

The advances in topological condensed matter physics enable the manipulation of classic waves in different ways, such as unidirectional propagation featuring the suppression of backscattering and the robustness against impurities and disorder, making it possible to endow classical phenomena with top...

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

January 03 2020

May 19 2020

Nature Materials

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Acta Materialia

Physical Review X

Physical Review Letters

Physical Review B Structure, Structural phase transitions, Mechanical properties, Defects

Modelling and Simulation in Materials Science and Engineering