The main focus of this paper is to introduce, in a thermodynamically consistent manner, an anisotropic interface energy into a phase field theory for phase transformations. Here we use a small strain formulation for simplicity, but we retain some geometric nonlinearities, which are necessary for int…

[Phys. Rev. B 92, 144106] Published Tue Oct 13, 2015

]]>Results for supercell-size convergence of formation energies and charge transition levels of vacancy complexes ${V}_{n}\phantom{\rule{0.28em}{0ex}}(1\le n\le 11)$ in crystalline Si are reported for the *ab initio* density functional theory (DFT) with generalized gradient approximation (GGA) pseudopotentials. When extrapolated to the dilute l…

[Phys. Rev. B 92, 144104] Published Mon Oct 12, 2015

]]>We use density functional theory to explain the preferred structure of partially reduced ${\mathrm{CeO}}_{2}\left(111\right)$. Low-energy ordered structures are formed when the vacancies are isolated (maximized intervacancy separation) and the size of the ${\mathrm{Ce}}^{3+}$ ions is minimized. Both conditions help minimize disruptions to th…

[Phys. Rev. B 92, 144105] Published Mon Oct 12, 2015

]]>We study the isotope effect on the temperature of the proton order/disorder phase transition between ice XI and ice Ih, using the quasiharmonic approximation combined with *ab initio* density functional theory calculations. We show that this method is accurate enough to obtain a phase-transition tempe…

[Phys. Rev. B 92, 134105] Published Fri Oct 09, 2015

]]>A pressure-induced phase transition, associated with the formation of cation-cation bonding, occurs in ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ by combining synchrotron x-ray diffraction in a diamond anvil cell and *ab initio* evolutionary calculations. The high-pressure phase has a monoclinic structure with a $C2/c$ space group, and it i…

[Phys. Rev. B 92, 134106] Published Fri Oct 09, 2015

]]>We present a low-temperature and high-pressure ultrasonic study of elastic properties of isotopic ${\mathrm{H}}_{2}\text{O-}{\mathrm{D}}_{2}\mathrm{O}$ solid solutions, comparing their properties with those of the isotopically pure ${\mathrm{H}}_{2}\mathrm{O}$ and ${\mathrm{D}}_{2}\mathrm{O}$ ices. Measurements were carried out for solid state amorphization (SSA) from 1h to high-density amorph…

[Phys. Rev. B 92, 134104] Published Thu Oct 08, 2015

]]>The nonequilibrium dynamics of diffusion-mediated plasticity and creep in materials subjected to constant load at high homologous temperatures is studied atomistically using phase field crystal (PFC) methods. Creep stress and grain size exponents obtained for nanopolycrystalline systems, $m\simeq 1.02$ and $\dots $

[Phys. Rev. B 92, 134103] Published Wed Oct 07, 2015

]]>Ammonium trichlorocuprate, ${\mathrm{NH}}_{4}{\mathrm{CuCl}}_{3}$, a member of the family of quantum antiferromagnets ${\mathrm{M}}_{3}{\mathrm{CuCl}}_{3}(\text{M}=\text{K},\text{Tl},{\mathrm{NH}}_{4}^{+})$, well known for its gapless magnetization with unusual plateaus, is shown here to exhibit ferroelectricity below 67 K based on anomalies of the specific heat and dielectric constant, along wi…

[Phys. Rev. B 92, 144103] Published Wed Oct 07, 2015

]]>We describe the results of first-principles calculations of the properties of oxygen vacancies in ${\mathrm{LaNiO}}_{3}$. We consider isolated oxygen vacancies, pairs of vacancies, and vacancies at finite concentrations that form oxygen-deficient phases of ${\mathrm{LaNiO}}_{3}$. The key electronic structure question we address is…

[Phys. Rev. B 92, 144102] Published Tue Oct 06, 2015

]]>When quartz is compressed at room temperature it retains its crystal structure at pressures well above its stability domain (0–2 GPa), and collapses into denser structures only when pressure reaches 20 GPa. Depending on the experimental conditions, pressure-induced densification can be accompanied b…

[Phys. Rev. B 92, 134102] Published Fri Oct 02, 2015

]]>Perovskite structured materials contain myriad tunable ordered phases of electronic and magnetic origin with proven technological importance and strong promise for a variety of energy solutions. An always-contributing influence beneath these cooperative and competing interactions is the lattice, who…

[Phys. Rev. B 92, 134101] Published Thu Oct 01, 2015

]]>The origin of compression-induced failure in brittle solids has been a subject of debate. Using *in situ*, high-speed, strain field mapping of a representative material, polymethylmethacrylate, we reveal that shock loading leads to heterogeneity in a compressive strain field, which in turn gives rise …

[Phys. Rev. B 92, 144101] Published Thu Oct 01, 2015

]]>We studied the structural modifications of a Pt/Co/Pt trilayer epitaxial film under ${\mathrm{Ga}}^{+}$ 30-keV ion irradiation by means of classical molecular dynamics and Monte Carlo simulations. The semiclassical tight-binding second-moment approximation potential was adjusted to reproduce the enthalpies of forma…

[Phys. Rev. B 92, 104109] Published Wed Sep 30, 2015

]]>Propagation of elastic waves in acoustic metamaterials based on locally resonant viscoelastic phononic crystals is discussed. A variational formulation of the complex band structure for in-plane polarized waves is proposed and used to formulate a finite element model. Two different types of locally …

[Phys. Rev. B 92, 104110] Published Wed Sep 30, 2015

]]>The system $\mathrm{HoA}{\mathrm{l}}_{3}{\left(\mathrm{B}{\mathrm{O}}_{3}\right)}_{4}$ has recently been found to exhibit a large magnetoelectric effect. To understand the mechanism, macroscopic and atomic level properties of $\mathrm{HoA}{\mathrm{l}}_{3}{\left(\mathrm{B}{\mathrm{O}}_{3}\right)}_{4}$ were explored by temperature and magnetic field dependent heat capacity measurements, pressure and temperature dependent x-ray…

[Phys. Rev. B 92, 104108] Published Wed Sep 23, 2015

]]>Stacking graphene sheets forms graphite. Two in-plane vibrational modes of graphite, ${E}_{1u}$ and ${E}_{2g}^{\left(2\right)}$, are derived from the graphene ${E}_{2g}$ mode, the shifts of which under compression are considered as results of the in-plane bond shortening. Values of the Grüneisen parameter have been reported to quanti…

[Phys. Rev. B 92, 094108] Published Tue Sep 22, 2015

]]>We study the charge-density-wave phase in ${\text{TiSe}}_{2}$ by using first-principles density functional theory calculations with the harmonic approximation for the electron-phonon coupling. We consider several local functionals and both experimental and theoretical cell parameters. The results obtained are ver…

[Phys. Rev. B 92, 094107] Published Mon Sep 21, 2015

]]>The local atomic and electronic structures around the dopants in Cr-doped $\left({\mathrm{Bi}}_{x}{\mathrm{Sb}}_{1-x}\right){}_{2}{\mathrm{Te}}_{3}$ are studied by x-ray absorption fine structure (XAFS) measurements and first-principles calculations. Both Cr and Bi are confirmed substituting Sb sites $({\mathrm{Cr}}_{\mathrm{Sb}}$ and ${\mathrm{Bi}}_{\mathrm{Sb}})$. The six nearest Te atoms around Cr move t…

[Phys. Rev. B 92, 100101(R)] Published Mon Sep 21, 2015

]]>Phase-field simulations demonstrate that the polarization order-parameter field in the Ginzburg-Landau-Devonshire model of rhombohedral ferroelectric ${\mathrm{BaTiO}}_{3}$ allows for an interesting linear defect, stable under simple periodic boundary conditions. This linear defect, here called the Ising line, can …

[Phys. Rev. B 92, 094106] Published Wed Sep 16, 2015

]]>The mechanical properties and electronic structure of recently synthesized $\mathrm{Pt}{\mathrm{N}}_{2}$, proposed as a potential candidate for superhard materials, have been investigated by means of density functional theory. Although it shows a clear band gap indicating a covalent bonding nature, the calculated shear modu…

[Phys. Rev. B 92, 104107] Published Wed Sep 16, 2015

]]>Extraordinary optical transmissions through metallic films with arrays of subwavelength holes have attracted much attention in the past few years, and surface plasmons are accepted as the key factor in their origin. Further studies showed that the abilities of surface plasmons can also be extended t…

[Phys. Rev. B 92, 104105] Published Mon Sep 14, 2015

]]>The quest for multiferroics with coexisting ferroic orders, such as ferroelectricity and (anti-)ferromagnetism, in a single phase continues to arouse interest by the promise of novel functions and technological device paradigms. However, the mutually exclusive mechanism of ferroelectricity and magne…

[Phys. Rev. B 92, 104106] Published Mon Sep 14, 2015

]]>We employ a real-space pseudopotential method to compute the structural energies of a prototypical metal-semiconductor interface. Specifically, we examine a Pb(111) film overlaid on a Si(111) substrate as a function of the metal thickness. For each layer of Pb, we fully relax the atomic coordinates …

[Phys. Rev. B 92, 094103] Published Fri Sep 11, 2015

]]>Nitrides in many ways are fascinating since they often appear as superconductors, high-energy density, and hard materials. Though there exist a large variety of nitrides, noble gas nitrides are missing in nature. Pursuit of noble gas nitrides has therefore become the subject of topical interests, bu…

[Phys. Rev. B 92, 094104] Published Fri Sep 11, 2015

]]>Highly accurate numerical simulations are employed to highlight the subtle but important differences in the mechanical stability of perfect crystalline solids versus amorphous solids. We stress the difference between strain values at which the shear modulus vanishes and strain values at which a plas…

[Phys. Rev. B 92, 094105] Published Fri Sep 11, 2015

]]>The properties of a new class of phosphorene nanotubes (PNT) are investigated by performing first-principles calculations. We demonstrate that it is advantageous to use blue phosphorene in order to make small nanotubes and propose a way to create low-energy PNTs by the inclusion of defect lines. Fiv…

[Phys. Rev. B 92, 104104] Published Fri Sep 11, 2015

]]>The second-order ordering transition of the ${\mathrm{AuAgZn}}_{2}$ alloy has been studied by coherent x-ray scattering. Within a few degrees above the critical temperature ${T}_{c}$, equilibrium critical fluctuations are observed together with some pretransitional local ordering connected to sample defects. The speckles …

[Phys. Rev. B 92, 094102] Published Wed Sep 09, 2015

]]>Cracks generate the largest strain gradients that any material can withstand. Flexoelectricity (coupling between strain gradient and polarization) must therefore play an important role in fracture physics. Here we use a self-consistent continuum model to evidence two consequences of flexoelectricity…

[Phys. Rev. B 92, 094101] Published Tue Sep 08, 2015

]]>The interband optical transitions in cube-on-cube-type epitaxial ferroelectric $\mathrm{NaNb}{\mathrm{O}}_{3}$ thin films and a reference antiferroelectric $\mathrm{NaNb}{\mathrm{O}}_{3}$ crystal are studied in the spectral range of 0.74–9 eV using variable-angle spectroscopic ellipsometry. The energies and the types of the transitions in the films…

[Phys. Rev. B 92, 104101] Published Wed Sep 02, 2015

]]>Based on a systematic first-principles study, the lowest-energy migration mechanisms and barriers for small vacancy-solute clusters $\left({V}_{n}{X}_{m}\right)$ are determined in $\alpha $-Fe for carbon, nitrogen, and oxygen, which are the most frequent interstitial solutes in several transition metals. We show that the dominant…

[Phys. Rev. B 92, 104102] Published Wed Sep 02, 2015

]]>Lattice stability and metastability, as well as melting, are important features of the physics and chemistry of dense hydrogen. Using *ab initio* molecular dynamics (AIMD), the classical superheating limit and melting line of metallic hydrogen are investigated up to 1.5 TPa. The computations show that…

[Phys. Rev. B 92, 104103] Published Wed Sep 02, 2015

]]>Interatomic potentials have been widely used in atomistic simulations such as molecular dynamics. Recently, frameworks to construct accurate interatomic potentials that combine a set of density functional theory (DFT) calculations with machine learning techniques have been proposed. One of these met…

[Phys. Rev. B 92, 054113] Published Mon Aug 31, 2015

]]>We present results of a temperature-dependent high-resolution synchrotron x-ray powder diffraction study of sequence of phase transitions in $\mathrm{N}{\mathrm{i}}_{2}\mathrm{MnGa}$. Our results show that the incommensurate martensite phase results from the incommensurate premartensite phase and not from the austenite phase assumed…

[Phys. Rev. B 92, 054112] Published Fri Aug 28, 2015

]]>Ferroelectricity in strain-free and strained double perovskite fluorides, ${\mathrm{Na}}_{3}{\mathrm{ScF}}_{6}$ and ${\mathrm{K}}_{2}{\mathrm{NaScF}}_{6}$, is investigated using first-principles density functional theory. Although the experimental room temperature crystal structures of these fluoroscandates are centrosymmetric, i.e., ${\mathrm{Na}}_{3}{\mathrm{ScF}}_{6}$ ($P{2}_{1}/n$) and ${\mathrm{K}}_{2}{\mathrm{Na\dots}}_{}$

[Phys. Rev. B 92, 054111] Published Thu Aug 27, 2015

]]>The lattice structure and symmetry of two-dimensional (2D) layered materials are of key importance to their fundamental mechanical, thermal, electronic, and optical properties. Raman spectroscopy, as a convenient and nondestructive tool, however, has its limitations in identifying all symmetry allow…

[Phys. Rev. B 92, 054110] Published Wed Aug 26, 2015

]]>Polarization switching kinetics is one of the key issues for future development of nanoelectronic devices based on ferroelectrics. Up to now, such kinetics still remains poorly studied despite its crucial impact on the device performances. Here, the switching mechanism in 11-nm-thick ferroelectric f…

[Phys. Rev. B 92, 060102(R)] Published Wed Aug 26, 2015

]]>The effects of normal compressive strain and in-plane strain on the structures of phosphorene have been investigated by using first-principles calculations. It is quite intriguing to find that a structural transformation from pristine Z-phosphorene to a new A-phosphorene occurs under the normal comp…

[Phys. Rev. B 92, 064114] Published Tue Aug 25, 2015

]]>In this work we aim to resolve the counterintuitive diffusion behavior of Fe and N atoms in an iron mononitride (FeN) thin film. It was observed that in spite of their larger size, Fe atoms tend to diffuse more rapidly than smaller N atoms. This only happens in the N-rich region of the Fe-N phase di…

[Phys. Rev. B 92, 054109] Published Mon Aug 24, 2015

]]>The sound velocity of Mo along the Hugoniot adiabat is calculated from first principles using density-functional theory based molecular dynamics. These data are compared to the sound velocity as measured in recent experiments. The theoretical and experimental Hugoniot and sound velocities are in ver…

[Phys. Rev. B 92, 060101(R)] Published Mon Aug 24, 2015

]]>We present a rigorous irreversible thermodynamics treatment of creep deformation of solid materials with interfaces described as geometric surfaces capable of vacancy generation and absorption and moving under the influence of local thermodynamic forces. The free energy dissipation rate derived in t…

[Phys. Rev. B 92, 064113] Published Mon Aug 24, 2015

]]>The local structures around Co and Fe in ${\mathrm{BiCo}}_{1-x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{3}$ (BCFO) have been determined element-selectively by means of extended x-ray absorption fine structure (EXAFS) measurements at the Co and Fe $K$ edges. In the tetragonal (T) phase at $x\le 0.63$, both Fe and Co ions are trivalent and locate in the ${\mathrm{O}}_{5}$ pyra…

[Phys. Rev. B 92, 054108] Published Fri Aug 21, 2015

]]>The structural transitions of the ground state of a system of repulsively interacting particles confined in a quasi-one-dimensional channel, and the effect of the interparticle interaction as well as the functional form of the confinement potential on those transitions are investigated. Although the…

[Phys. Rev. B 92, 064112] Published Fri Aug 21, 2015

]]>Structural changes of ${\mathrm{Li}}_{2}{\mathrm{C}}_{2}$ under pressure were studied by synchrotron x-ray diffraction in a diamond anvil cell under hydrostatic conditions and by using evolutionary search methodology for crystal structure prediction. We show that the high-pressure polymorph of ${\mathrm{Li}}_{2}{\mathrm{C}}_{2}$, which forms from the $Immm$ gr…

[Phys. Rev. B 92, 064111] Published Wed Aug 19, 2015

]]>Phase competition and the subsequent phase selection are important characteristics of alloy systems exhibiting numerous states of distinct symmetry but comparable energy. The stoichiometric ${\mathrm{Co}}_{2}\mathrm{NiGa}$ Heusler alloy exhibits a martensitic transformation with concomitant reduction in symmetry from an aus…

[Phys. Rev. B 92, 054107] Published Thu Aug 13, 2015

]]>The phase diagram of solid oxygen in the magnetic-field-temperature ($B-T$) plane is revealed by magnetization and magnetotransmission measurements. The high-field phase of solid oxygen, which we term the $\theta $ phase, is induced at the temperature below 42 K. The transition fields at the $\alpha -\theta $ and $\beta -\theta $ trans…

[Phys. Rev. B 92, 064109] Published Thu Aug 13, 2015

]]>We have explored the high-pressure structural, vibrational, electronic, and magnetic behavior of the multiferroic $\mathrm{CoC}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$ spinel up to 30 GPa by means of x-ray diffraction, Raman spectroscopy, and density functional theory calculations. Our investigations revealed a reversible tetragonal distortion …

[Phys. Rev. B 92, 064108] Published Wed Aug 12, 2015

]]>From the energies of various noncollinearly ordered spin configurations of ${\mathrm{YMnO}}_{3}$ obtained using first-principles density functional theory and spin-orbit coupling, we demonstrate a remarkable magnetocrystalline anisotropy in the ordering of spins of ${\mathrm{Mn}}^{3+}$ ions. We find that these spins are confined i…

[Phys. Rev. B 92, 054106] Published Tue Aug 11, 2015

]]>Using *ab initio* calculations and symmetrized plane waves, we analyze the basal-plane generalized stacking fault energies in pure Mg and Mg-Y alloys and show that the knowledge of energies of only five specific points is sufficient to accurately predict the core structures and Peierls stresses of $\langle a\rangle $…

[Phys. Rev. B 92, 064107] Published Tue Aug 11, 2015

]]>The quasiharmonic (QH) approximation uses harmonic vibrational frequencies ${\omega}_{Q,H}\left(V\right)$ computed at volumes $V$ near ${V}_{0}$ where the Born-Oppenheimer (BO) energy ${E}_{\mathrm{el}}\left(V\right)$ is minimum. When this is used in the harmonic free energy, QH approximation gives a good zeroth order theory of thermal expansion and first-o…

[Phys. Rev. B 92, 064106] Published Mon Aug 10, 2015

]]>We report systematic diffuse x-ray scattering measurements of the elastic strain fields generated by oxygen vacancies in strained bulk ${\mathrm{SrTiO}}_{3}$ crystals. Diffuse x-ray scattering has been used for decades to measure the elastic strain fields generated by point defects based on the assumptions that the…

[Phys. Rev. B 92, 064105] Published Fri Aug 07, 2015

]]>The structural transformation of multiferroic ${\mathrm{EuTiO}}_{3}$ has been intensively investigated by synchrotron x-ray diffraction at pressures up to 50.3 GPa and temperatures from 50 to 500 K. A pressure-induced antiferrodistortive phase transition from cubic $Pm\overline{3}m$ to tetragonal $I4/mcm$ space group has been ob…

[Phys. Rev. B 92, 064102] Published Thu Aug 06, 2015

]]>Modeling of nanostructure evolution in solids requires comprehensive data on the properties of defects such as the vacancy and foreign atoms. Since most processes occur at elevated temperatures, not only the energetics of defects in the ground state, but also their temperature-dependent free energie…

[Phys. Rev. B 92, 064103] Published Thu Aug 06, 2015

]]>Single spin carrying defects are key elements in quantum information and nanosensing technology with the nitrogen-vacancy (NV) center in diamond being the outstanding example. In a combined electron paramagnetic resonance and first-principles modeling study we verify the existence of such NV centers…

[Phys. Rev. B 92, 064104] Published Thu Aug 06, 2015

]]>Biaxial strain in coherent epitaxial thin films can have a pronounced effect on the point-defect profile in the films' material. Detailed fundamental knowledge of the interaction of strain with point defects is crucial to understanding the stoichiometry and resulting properties of strained thin film…

[Phys. Rev. B 92, 054103] Published Wed Aug 05, 2015

]]>Using the dynamical matrix of a crystal obtained from *ab initio* calculations, we have evaluated the strength of the dynamic flexoelectric effect and found it comparable to that of the static bulk flexoelectric effect, in agreement with earlier order-of-magnitude estimates. We also propose a method o…

[Phys. Rev. B 92, 054104] Published Wed Aug 05, 2015

]]>We present here a first-principles study of the ternary compounds formed by Ni, In, and As, a material of great importance for self-aligned metallic contacts in next-generation InAs-based MOS transistors. The approach we outline is general and can be applied to study the crystal structure and proper…

[Phys. Rev. B 92, 054105] Published Wed Aug 05, 2015

]]>Ferroelectric thin films are considered to be among the top candidates for room-temperature electrocaloric materials as they exhibit excellent electric properties and allow application of record high electric fields. At the same time, downsizing of ferroelectric electrocalorics brings about an unwan…

[Phys. Rev. B 92, 064101] Published Wed Aug 05, 2015

]]>Hexagonal $\mathrm{ErFe}{\mathrm{O}}_{3}$ thin films fabricated by a pulsed laser deposition method were investigated by x-ray diffraction (XRD) and transmission electron microscopy. No structural phase transition was observed between 20 and 900 K. Ferroelectric $D-E$ hysteresis loops were obtained at room temperature using t…

[Phys. Rev. B 92, 054101] Published Mon Aug 03, 2015

]]>The pressure-induced structural phase transition in the intermediate-valence compound CeNi has been investigated by x-ray and neutron powder diffraction techniques. It is shown that the structure of the pressure-induced CeNi phase (phases) can be described in terms of the $Pnma$ space group. Equations…

[Phys. Rev. B 92, 054102] Published Mon Aug 03, 2015

]]>EuTiO${}_{3}$ has been attracting considerable attention due to its large magnetoelectric effect and its potential for future applications. In this work the authors focus on the structural phase transition that bears resemblance to the prototypical phase transition in isostructural SrTiO${}_{3}$ but takes place at much higher temperatures ${T}_{S}$. The authors perform a detailed study of poly- and single-crystalline EuTiO${}_{3}$ and EuTi${}_{1-x}$Nb${}_{x}$O${}_{3}$ using synchrotron X-ray diffraction, Resonant Ultrasound Spectroscopy, and magnetization measurements. They find an unexpectedly rapid increase of ${T}_{S}$ when EuTiO${}_{3}$ is doped with niobium. Another notable result of the Nb doping, which is confirmed in this study for single-crystalline samples, is an unusual transformation of the low-temperature phase from an antiferromagnetic to ferromagnetic state at $x=0.1$.

[Phys. Rev. B 92, 024109] Published Thu Jul 30, 2015

]]>The $\mathrm{H}{\mathrm{o}}_{2}\mathrm{T}{\mathrm{i}}_{2}{\mathrm{O}}_{7},\mathrm{E}{\mathrm{r}}_{2}\mathrm{T}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$, and $\mathrm{Y}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{i}}_{2}{\mathrm{O}}_{7}$ pyrochlores were studied by synchrotron x-ray diffraction to determine whether the (002) peak, forbidden in the pyrochlore space group $Fd-3m$ but observed in single crystal neutron scattering measurements, is present due to a deviation of their pyrochlore structur…

[Phys. Rev. B 92, 024110] Published Thu Jul 30, 2015

]]>The high-pressure behavior of natural henritermierite garnet with close to end-member composition ${\mathrm{Ca}}_{3}{\mathrm{Mn}}_{2}\left[{\mathrm{SiO}}_{4}{]}_{2}\right[{\mathrm{O}}_{4}{\mathrm{H}}_{4}]$ was studied at pressures up to 80 GPa using single-crystal synchrotron x-ray diffraction, Raman spectroscopy, and quantum-mechanical calculations based on density functional theory. …

[Phys. Rev. B 92, 014117] Published Wed Jul 29, 2015

]]>Utilizing single-crystal synchrotron x-ray scattering, we observe distorted ${\text{CuO}}_{2}$ planes in the electron-doped superconductor ${\mathrm{Pr}}_{1-x}{\mathrm{LaCe}}_{x}{\mathrm{CuO}}_{4+\delta},x$ = 0.12. Resolution-limited rods of scattering are indicative of a long-range two-dimensional $2\sqrt{2}\times 2\sqrt{2}$ superstructure in the $a-b$ plane, adhering to planar spac…

[Phys. Rev. B 92, 014118] Published Wed Jul 29, 2015

]]>Taking advantage of the new opportunities provided by x-ray free electron laser (FEL) sources when coupled to a long laser pulse as available at the Linear Coherent Light Source (LCLS), we have performed x-ray absorption near-edge spectroscopy (XANES) of laser shock compressed iron up to 420 GPa ($\pm \mathrm{5\dots}$

[Phys. Rev. B 92, 024108] Published Wed Jul 29, 2015

]]>The Jahn-Teller effect is a fascinating and ubiquitous phenomenon in modern quantum physics and chemistry. We propose a class of oxides with a melilite structure ${\mathrm{Ba}}_{2}T{\mathrm{Ge}}_{2}{\mathrm{O}}_{7}$ $(T=\text{V},\text{Ni})$ where Jahn-Teller distortions are mainly responsible for the appearance of electric polarization. At the heart of the p…

[Phys. Rev. B 92, 014116] Published Mon Jul 27, 2015

]]>In this Comment we discuss recent results presented by Nguyen *et al.* on shock compressed molybdenum up to 438 GPa [Phys. Rev. B **89**, 174109 (2014)]. The aim of Nguyen's article is to show that there is no phase transition near 210 GPa. We propose instead an interpretation of their data that this mate…

[Phys. Rev. B 92, 026101] Published Mon Jul 27, 2015

]]>We respond to the Comment by Errandonea *et al.* [Phys. Rev. B **92**, 026101 (2015)] on their reinterpretation of our published data [Nguyen *et al.*, Phys. Rev. B **89**, 174109 (2014)]. In the original paper, we argued that there is no solid-solid phase transition along the Hugoniot at 2.1 Mbars. There is, …

[Phys. Rev. B 92, 026102] Published Mon Jul 27, 2015

]]>In this work we performed 2.5-dimensional (2.5D) dislocation dynamics simulations coupling climb with the glide dislocation motion to model the creep behavior of olivine, one of the main component of the Earth's upper mantle. In particular, we present an application of this method to determine the c…

[Phys. Rev. B 92, 014115] Published Thu Jul 23, 2015

]]>The preparations of single (monolayer) and bulk carbides on the $\mathrm{Mo}\left(110\right)$ and $\mathrm{Mo}\left(100\right)$ single crystals are followed *in situ* at 1200 K using synchrotron-based high-resolution x-ray photoelectron spectroscopy of the $\mathrm{C}\phantom{\rule{0.28em}{0ex}}1s$ and core Mo $3{d}_{5/2}$ levels. By comparing the experimental results to first principles c…

[Phys. Rev. B 92, 014114] Published Wed Jul 22, 2015

]]>The irreversibility of the martensite transition in magnetic shape memory alloys (MSMAs) with respect to the external magnetic field is one of the biggest challenges that limits their application as giant caloric materials. This transition is a magnetostructural transition that is accompanied with a…

[Phys. Rev. B 92, 020105(R)] Published Wed Jul 22, 2015

]]>The electronic structure of thallium rhenium oxide (${\mathrm{TlReO}}_{4}$) at room temperature is explored as a function of applied pressure using a diamond-anvil cell and high-resolution x-ray absorption spectroscopy. We show possible evidence of charge transfer from the thallium to the rhenium atom in the high-p…

[Phys. Rev. B 92, 014113] Published Tue Jul 21, 2015

]]>The nucleation, growth, and propagation of like-spin domains in spin-crossover materials was investigated during the relaxation process of a metastable HS state at low temperature using an electroelastic model running on a deformable two-dimensional square lattice. We distinguish the onset of patter…

[Phys. Rev. B 92, 014111] Published Mon Jul 20, 2015

]]>The experimental observation of an efficient second-order nonlinearity with dominating frequency upconversion is reported for one-dimensional (1D) guided elastic waves localized at solid edges. These 1D acoustic wedge waves are a fundamental type of elastic wave with a phase velocity below that of s…

[Phys. Rev. B 92, 014112] Published Mon Jul 20, 2015

]]>High-performance refractory materials play an important role in applications ranging from gas turbines to heat shields for hypersonic vehicles. The authors carried out an extensive first-principles investigation into the melting temperatures of the refractory Hf-C and Hf-Ta-C systems, which hold the highest melting temperatures known to date, and identified the major factors that contribute to the high melting temperatures. A new class of materials were proposed and explored, which, according to the calculation, may increase the current melting point record by up to 200 K. This work demonstrates the feasibility and usefulness of large-scale first-principles calculations for high-throughput materials screening on a high-level thermodynamic property.

[Phys. Rev. B 92, 020104(R)] Published Mon Jul 20, 2015

]]>A range of compelling information on the local structure and dynamics of the ferroelectric perovskite-type $\left({\mathrm{ABO}}_{3}\right)$ system $(1-x){\mathrm{PbTiO}}_{3}-x{\mathrm{BiScO}}_{3}$ has been revealed through analyzing room-temperature x-ray pair distribution functions and temperature-dependent Raman scattering data for compositions ranging…

[Phys. Rev. B 92, 024107] Published Wed Jul 15, 2015

]]>Shock-induced freezing in liquids has long been a subject of interest as well as mystery. With large-scale molecular dynamics simulations, we demonstrate that homogeneous crystal nucleation in liquid Cu can be realized under effective supercooling $\left(\theta \right)$, via quasi-isentropic compression or ramp wave l…

[Phys. Rev. B 92, 014108] Published Mon Jul 13, 2015

]]>Complex metallic alloys having isolated transition-metal elements in the surface layer have been reported to work well as selective hydrogenation catalysts. We report an experimental determination of the surface structure of one such compound $\mathrm{A}{\mathrm{l}}_{13}\mathrm{F}{\mathrm{e}}_{4}\left(010\right)$. The structure was determined using low-ener…

[Phys. Rev. B 92, 014109] Published Mon Jul 13, 2015

]]>We present a comprehensive set of first-principles electronic structure calculations of the properties of substitutional transition metal solutes and point defects in austenite (face-centered cubic, paramagnetic Fe). Clear trends were observed in these quantities across the transition metal series, …

[Phys. Rev. B 92, 014110] Published Mon Jul 13, 2015

]]>Phase transformations in metallic grain boundaries (GBs) present significant fundamental interest in the context of thermodynamics of low-dimensional physical systems. We report on atomistic computer simulations of the Cu-Ag system that provide direct evidence that GB phase transformations in a sing…

[Phys. Rev. B 92, 020103(R)] Published Mon Jul 13, 2015

]]>The composition-dependent crystal structure, elastic modulus, phase stability, and magnetic property of ${\mathrm{Ni}}_{2-x}{\mathrm{Co}}_{x}{\mathrm{Mn}}_{1.60}{\mathrm{Sn}}_{0.40}\phantom{\rule{4.pt}{0ex}}\left(0\le x\le 0.50\right)$ are studied by using first-principles calculations in combination with atomistic spin dynamics method. It is shown that the present lattice parameters and Curie temp…

[Phys. Rev. B 92, 024105] Published Mon Jul 13, 2015

]]>We present an automated scheme to systematically sample energy landscapes of crystalline solids, based on the ideas of metadynamics and evolutionary algorithms. Phase transitions are driven by the evolution of the order parameter (in this case, 6-dimensional order parameters composed of cell vectors…

[Phys. Rev. B 92, 024106] Published Mon Jul 13, 2015

]]>We used density functional theory (DFT) calculations to model the interaction of hydrogen atoms and molecules with strained bonds and neutral oxygen vacancies in amorphous silica $\left({\text{a-SiO}}_{2}\right)$. The results demonstrate that the interaction of atomic hydrogen with strained Si–O bonds in defect-free ${\text{a-SiO}}_{2}$ …

[Phys. Rev. B 92, 014107] Published Fri Jul 10, 2015

]]>The physical state and properties of silicates at conditions encountered in the cores of gas giants, ice giants, and of Earth-like exoplanets now discovered with masses up to several times the mass of the Earth remain mostly unknown. Here, we report on theoretical predictions of the properties of si…

[Phys. Rev. B 92, 014105] Published Wed Jul 08, 2015

]]>Data-driven approaches are particularly useful for computational materials discovery and design as they can be used for rapidly screening over a very large number of materials, thus suggesting lead candidates for further in-depth investigations. A central challenge of such approaches is to develop a…

[Phys. Rev. B 92, 014106] Published Wed Jul 08, 2015

]]>We propose a local real-space formulation for orbital-free density functional theory (DFT) with density dependent kinetic energy functionals and a unified variational framework for computing the configurational forces associated with geometry optimization of both internal atomic positions as well as…

[Phys. Rev. B 92, 014104] Published Tue Jul 07, 2015

]]>The morphology transition from the thermodynamically favorable to the unfavorable phase during growth of freestanding copper nanoclusters is studied by molecular dynamics simulations. We give a detailed description of the kinetics and thermodynamics of the process. A universal mechanism of a solid-s…

[Phys. Rev. B 92, 020102(R)] Published Tue Jul 07, 2015

]]>The thermal evolution of electronic order in the complex Verwey ground state of magnetite $\left(\mathrm{F}{\mathrm{e}}_{3}{\mathrm{O}}_{4}\right)$ has been determined through 22 high-accuracy synchrotron x-ray structure refinements using three $10\u201340\phantom{\rule{0.16em}{0ex}}\mu \mathrm{m}$ grains of stoichiometric magnetite. A robust fitting function is introduced to extract values of …

[Phys. Rev. B 92, 024104] Published Tue Jul 07, 2015

]]>Precise characterization of a system's Hamiltonian is crucial to its high-fidelity control that would enable many quantum technologies, ranging from quantum computation to communication and sensing. In particular, nonsecular parts of the Hamiltonian are usually more difficult to characterize, even i…

[Phys. Rev. B 92, 020101(R)] Published Mon Jul 06, 2015

]]>X-ray absorption near-edge spectroscopy, photoluminescence, cathodoluminescence, and Raman spectroscopy have been used to investigate the chemical states of nitrogen dopants in ZnO nanowires. It is found that nitrogen exists in multiple states: ${\mathrm{N}}_{\mathrm{O}},\phantom{\rule{0.16em}{0ex}}{\mathrm{N}}_{\mathrm{Zn}}$, and loosely bound ${\mathrm{N}}_{2}$ molecule. The results esta…

[Phys. Rev. B 92, 024103] Published Mon Jul 06, 2015

]]>Density functional theory and group-theoretical methods are used to explore the origin for ferroelectricity in cation ordered ${\mathrm{LaSrMnO}}_{4}$ with the Ruddlesden-Popper structure. The equilibrium phase exhibits the polar $Pca{2}_{1}$ space group where small polar displacements of ${d}^{4}\phantom{\rule{0.28em}{0ex}}{\mathrm{Mn}}^{3+}$ coexist with antiferrodist…

[Phys. Rev. B 92, 014102] Published Thu Jul 02, 2015

]]>The elastic moduli, elastic anisotropy coefficients, sound velocities and Poisson's ratio of hcp solid helium have been calculated using density functional theory in generalized gradient approximation (up to 30 TPa), and pair + triple semiempirical potentials (up to 100 GPa). Zero-point vibrations h…

[Phys. Rev. B 92, 024102] Published Thu Jul 02, 2015

]]>Silicon materials play a key role in many technologically relevant fields, ranging from the electronic to the photovoltaic industry. A systematic search for silicon allotropes was performed by employing a modified *ab initio* minima hopping crystal structure prediction method. The algorithm was optimi…

[Phys. Rev. B 92, 014101] Published Wed Jul 01, 2015

]]>We investigated the crystal structure and lattice excitations of the ternary intermetallic stannide ${\mathrm{Ca}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Sn}}_{13}$ using neutron and x-ray scattering techniques. For $T>{T}^{*}\approx 38$ K, the x-ray diffraction data can be satisfactorily refined using the space group $Pm\overline{3}n$. Below ${T}^{*}$, the crystal structure is mod…

[Phys. Rev. B 92, 024101] Published Wed Jul 01, 2015

]]>An atomistic numerical scheme is developed and used to study the prototype of relaxor ferroelectrics, that is ${\mathrm{PbMg}}_{1/3}{\mathrm{Nb}}_{2/3}{\mathrm{O}}_{3}$ (PMN), at finite temperatures. This scheme not only reproduces known complex macroscopic properties of PMN, but also provides a deep microscopic insight into this puzzling sys…

[Phys. Rev. B 91, 214117] Published Tue Jun 30, 2015

]]>The highly complex structure-property interrelationship in the lead-free piezoelectric $\left(x\right)\phantom{\rule{0.16em}{0ex}}\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2}\mathrm{Ti}{\mathrm{O}}_{3}\phantom{\rule{4.pt}{0ex}}\text{\u2212}\phantom{\rule{4.pt}{0ex}}(1-x)\phantom{\rule{0.28em}{0ex}}\mathrm{BaTi}{\mathrm{O}}_{3}$ is a subject of considerable contemporary debate. Using comprehensive x-ray, neutron diffraction, dielectric, and ferroelectric studies, we have shown the existence of a new criticali…

[Phys. Rev. B 91, 214116] Published Mon Jun 29, 2015

]]>Dislocations are central to the understanding of plasticity in metals. Using density functional theory the authors show that interstitial carbon atoms in ferritic steels stabilize a dislocation core configuration called a hard core which is otherwise unstable. Since, as they also show, at equilibrium all dislocations are expected to be fully decorated by carbon atoms, this has important implications for the understanding of plasticity in ferritic steels. It is expected that the picture developed here could also be applicable to other solutes besides carbon and to other metals besides iron.

[Phys. Rev. B 91, 220102(R)] Published Mon Jun 29, 2015

]]>We experimentally demonstrate a three-dimensional x-ray ptychography in combination with precession measurements that can reconstruct multisection images of optically thick objects. We collect a tilt-series ptychographic diffraction data set of a four-layered object and then successfully reconstruct…

[Phys. Rev. B 91, 214114] Published Thu Jun 25, 2015

]]>Using an optical interferometric method, the cavitation density of bulk superfluid helium at $T=0.96\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is measured and found to be ${\rho}_{\mathrm{cav}}=0.1338\pm 0.0002\phantom{\rule{0.28em}{0ex}}\mathrm{g}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{-3}$. A well-established equation of state for liquid helium at negative pressures converts this to the cavitation pressure ${P}_{\mathrm{cav}}=-5.1\pm 0.1\phantom{\rule{0.28em}{0ex}}\mathrm{bars}$. This cavi…

[Phys. Rev. B 91, 214115] Published Thu Jun 25, 2015

]]>A recently discovered phase of orthorhombic iron carbide o-${\mathrm{Fe}}_{7}{\mathrm{C}}_{3}$ [Prescher *et al.*, Nat. Geosci. **8**, 220 (2015)] is assessed as a potentially important phase for interpretation of the properties of the Earth's core. In this paper, we carry out first-principles calculations on o-${\mathrm{Fe}}_{7}{\mathrm{C}}_{3}$, finding properti…

[Phys. Rev. B 91, 214112] Published Wed Jun 24, 2015

]]>We present a theoretical study of the electron transmission through the AB-BA stacking boundary in multilayer graphenes. Using the tight-binding model and the transfer matrix method, we calculate the electron transmission probability through the boundary as a function of electron Fermi energy in mul…

[Phys. Rev. B 91, 214113] Published Wed Jun 24, 2015

]]>