We investigate the surface stress of solid-liquid diffusive interfaces at equilibrium using the phase field crystal model in two dimensions. To analytically study the surface energy dependence on elastic strains, we employ the amplitude equation formalism and recast the free energy functional in ter...

[Phys. Rev. B 96, 214106] Published Fri Dec 15, 2017

]]>The paraelectric-ferroelectric transition in $\mathrm{CdTi}{\mathrm{O}}_{3}$ has been monitored using high-resolution neutron diffraction data. This necessitated preparing a sample enriched in ${}^{114}\mathrm{Cd}$. A subtle, but significant, anisotropy in the thermal expansion of the lattice parameters for $\mathrm{CdTi}{\mathrm{O}}_{3}$ associated with the trans...

[Phys. Rev. B 96, 214105] Published Wed Dec 13, 2017

]]>Although many works have been devoted to the order-disorder transition in carbon-supersaturated α-Fe, all seem to have overlooked the temperature hysteresis phenomenon occurring around the critical temperature. It is shown, from a mean-field model based on the elasticity theory of point defects, tha...

[Phys. Rev. B 96, 214104] Published Tue Dec 12, 2017

]]>We use scattering theory to study the spatial resolution achievable in vibrational energy loss spectroscopy using a focused beam of high-energy ($\sim 100$ keV) electrons. We first outline a theory for calculating vibrational-spectroscopic images of crystalline or noncrystalline materials at nanometer spa...

[Phys. Rev. B 96, 224102] Published Mon Dec 11, 2017

]]>Hard-mode Raman spectroscopy was applied to analyze the temperature-induced transformation processes in perovskite-type $\left({\mathrm{ABO}}_{3}\right)$ single crystals of $\left(1\text{\u2212}x\right){\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}{\mathrm{TiO}}_{3}\text{\u2212}x{\mathrm{BaTiO}}_{3}$ (NBT-$x\mathrm{BT})$ in a wide temperature range between 100 and 1010 K and a composition range of $x=0\u20130.074$ across the morphotropic phas...

[Phys. Rev. B 96, 214102] Published Fri Dec 08, 2017

]]>We present a detailed structure solution for the $16\text{\u2212}\AA $ decagonal quasicrystal in the Al-Pd-Mn system by means of cluster decoration and *ab initio* energy minimization. It is based on structure models of the $\varepsilon $ and other approximant phases. The $\varepsilon $ phases can be represented as subsets of a hexagon-boat-st...

[Phys. Rev. B 96, 214103] Published Fri Dec 08, 2017

]]>The phase diagram of 1$T$-TaS${}_{2}$ involves many different solid-state phases, including several different kinds of charge-density-wave (CDW) phase both commensurate and incommensurate with the underlying lattice. Recent experiments have shown that it is possible to drive transitions between these phases with intense femtosecond pulses of light. This work focuses on the light-driven transition from the nearly commensurate CDW phase to the incommensurate phase, using time-resolved x-ray diffraction. The authors find that the new incommensurate domains grow in a self-similar way. They also employ a double-pump method to study the dynamics and stability of the novel incommensurate phase during growth.

[Phys. Rev. B 96, 224101] Published Wed Dec 06, 2017

]]>All carbon materials, e.g., amorphous carbon (a-C) coatings and ${\mathrm{C}}_{60}$ fullerene thin films, play an important role in short-wavelength free-electron laser (FEL) research motivated by FEL optics development and prospective nanotechnology applications. Responses of a-C and ${\mathrm{C}}_{60}$ layers to the extreme ultr...

[Phys. Rev. B 96, 214101] Published Mon Dec 04, 2017

]]>The plastic deformation of crystalline materials is usually modeled as smoothly progressing in space and time, yet modern studies show intermittency in the deformation dynamics of single-crystals arising from avalanche behavior of dislocation ensembles under uniform applied loads. However, once the ...

[Phys. Rev. B 96, 174116] Published Thu Nov 30, 2017

]]>We define a structural parameter, called atomic bond length deviation ($\mathrm{BL}{\mathrm{D}}_{\mathrm{i}}$), to characterize structural heterogeneity of CuZr melt and metallic glass (MG). Molecular dynamics simulations have been performed to explore the average $\mathrm{BL}{\mathrm{D}}_{\mathrm{i}}$ of the system evolution with temperature during $\mathrm{C}{\mathrm{u}}_{64}\mathrm{Z}{\mathrm{r}}_{36}$ and $\mathrm{C}{\mathrm{u}}_{\mathrm{5...}}$

[Phys. Rev. B 96, 174112] Published Mon Nov 27, 2017

]]>From the new infrared (IR) reflectivity and time-domain terahertz spectra combined with available high-frequency dielectric data above the megahertz range in a broad temperature range of 10 to 900 K, a full picture of the soft- and central-mode behavior in the classical relaxor ferroelectric $\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/\mathrm{...}}$

[Phys. Rev. B 96, 174113] Published Mon Nov 27, 2017

]]>We report the results of ambient temperature high-pressure synchrotron-based x-ray diffraction, Raman, and electrical resistance study of $\mathrm{Cs}{\mathrm{I}}_{3}$ up to 29, 25, and 8 GPa, respectively, and confirm three-phase transitions under quasihydrostatic conditions. The ambient orthorhombic (space group (SG): *Pnm...*

[Phys. Rev. B 96, 174114] Published Mon Nov 27, 2017

]]>The influence of nanoscale cavities on the fracture of the $\mathrm{\Sigma}33\left\{554\right\}\left[110\right]$ symmetrical tilt grain boundary is studied by atomistic simulations. The crack crystallography is chosen such that dislocation emission is easy. A transition from a ductile behavior of the tip to a brittle one is obtained for a...

[Phys. Rev. B 96, 174115] Published Mon Nov 27, 2017

]]>Pressure-induced polarization switching in ferroelectric thin films has emerged as a powerful method for domain patterning, allowing us to create predefined domain patterns on free surfaces and under thin conductive top electrodes. However, the mechanisms for pressure-induced polarization switching ...

[Phys. Rev. B 96, 184109] Published Mon Nov 27, 2017

]]>The dynamics of the phase transition in antiferroelectric ${\mathrm{PbZrO}}_{3}$ which is the subject of a decades-long debate, is examined using first-principles-based simulations. This is achieved through the development of a computational approach that allows calculations of generalized complex susceptibilities...

[Phys. Rev. B 96, 184110] Published Mon Nov 27, 2017

]]>Lead-halide organic-inorganic perovskites consist of an inorganic host framework with an organic molecule occupying the interstitial space. The structure and dynamics of these materials have been heavily studied recently due to interest in their exceptional photovoltaic properties. We combine inelas...

[Phys. Rev. B 96, 174111] Published Wed Nov 22, 2017

]]>We present an extended Tersoff potential for boron nitride (BN-ExTeP) for application in large scale atomistic simulations. BN-ExTeP accurately describes the main low energy B, N, and BN structures and yields quantitatively correct trends in the bonding as a function of coordination. The proposed ex...

[Phys. Rev. B 96, 184108] Published Mon Nov 20, 2017

]]>The work describes a first-principles-based computational strategy for studying structural phase transitions, and in particular, for determination of the so-called Landau-Devonshire potential—the classical zero-temperature limit of the Gibbs energy, expanded in terms of order parameters. It exploits...

[Phys. Rev. B 96, 174110] Published Fri Nov 17, 2017

]]>The local dynamics of the lead-free relaxor $0.964{\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2}{\mathrm{TiO}}_{3}-0.036{\mathrm{BaTiO}}_{3}$ (NBT-3.6BT) have been investigated by a combination of quasielastic neutron-scattering (QENS) and *ab initio* molecular dynamics simulations. In a previous paper, we were able to show that the tetragonal platelets in the micro...

[Phys. Rev. B 96, 184107] Published Wed Nov 15, 2017

]]>Measurement of the Hugoniot and sound velocity provides information on the bulk modulus and Grüneisen parameter of a material at extreme conditions. The capability to launch multilayered (copper/aluminum) flyer plates at velocities in excess of 20 km/s with the Sandia Z accelerator has enabled high-...

[Phys. Rev. B 96, 174109] Published Mon Nov 13, 2017

]]>The mechanical force from light—radiation pressure—provides an intrinsically nonlinear interaction. Consequently, optomechanical systems near their steady state, such as the canonical optical spring, can display nonanalytic behavior as a function of external parameters. This nonanalyticity, a key fe...

[Phys. Rev. B 96, 184106] Published Mon Nov 13, 2017

]]>We investigate the effects of Fe and Co substitutions on the phase stability of the martensitic phase and mechanical, electronic, and magnetic properties of the magnetic shape memory system ${\mathrm{Mn}}_{2}\mathrm{NiGa}$ by first-principles density functional theory calculations. The evolution of these aspects upon substi...

[Phys. Rev. B 96, 174107] Published Fri Nov 10, 2017

]]>Neutron and x-ray scattering measurements were performed on $\left(\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2}\right)\mathrm{Ti}{\mathrm{O}}_{3}\text{\u2212}x\phantom{\rule{0.28em}{0ex}}\mathrm{at}\%\mathrm{BaTi}{\mathrm{O}}_{3}$ (NBT-$x\mathrm{BT}$) single crystals ($x=4$, 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to ...

[Phys. Rev. B 96, 174108] Published Fri Nov 10, 2017

]]>A force-matched spline-based empirical potential based on the modified embedded-atom method is fit to an extensive database of highly converged density functional theory calculations for titanium-niobium alloys with an evolutionary algorithm. Consistency with experiment and existing models is verifi...

[Phys. Rev. B 96, 184105] Published Fri Nov 10, 2017

]]>We present high-energy x-ray diffraction studies on the structural phases of an optimal high-${T}_{c}$ superconductor ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4+y}$ tailored by co-hole-doping. This is specifically done by varying the content of two very different chemical species, Sr and O, respectively, in order to study the influence o...

[Phys. Rev. B 96, 174106] Published Thu Nov 09, 2017

]]>First-principles molecular dynamics (FPMD) simulations are performed on 6 and 12% Na in dense liquid N. A detailed description of structural and electronic properties leading to an understanding of the effect of Na doping on the polymerization phase transition of N is presented. Compression of the m...

[Phys. Rev. B 96, 184104] Published Thu Nov 09, 2017

]]>Under mechanical loading, crystalline solids deform elastically, and subsequently yield and fail via plastic deformation. Thus crystalline materials experience two mechanical regimes: elasticity and plasticity. Here, we provide numerical and theoretical evidence to show that metal nanoplates exhibit...

[Phys. Rev. B 96, 184103] Published Tue Nov 07, 2017

]]>We study the two-step spin crossover in a double-layered elastic model based on transition metal complexes each taking high spin (HS) and low spin (LS) states. Here, only the simplest elastic interactions between adjacent molecules are considered, and the system is exposed to the external pressure w...

[Phys. Rev. B 96, 174104] Published Mon Nov 06, 2017

]]>The carbon vacancy in $4H$-SiC is a powerful minority carrier recombination center in as-grown material and a major cause of degradation of SiC-based devices. Despite the extensiveness and maturity of the literature regarding the characterization and modeling of the defect, many fundamental questions ...

[Phys. Rev. B 96, 174105] Published Mon Nov 06, 2017

]]>We measure the onset of decomposition of silicon carbide, SiC, to silicon and carbon (e.g., diamond) at high pressures and high temperatures in a laser-heated diamond-anvil cell. We identify decomposition through x-ray diffraction and multiwavelength imaging radiometry coupled with electron microsco...

[Phys. Rev. B 96, 174102] Published Fri Nov 03, 2017

]]>Direct experimental insights into the structural and dynamical mechanisms for ferroelectric β to paraelectric α phase transition in a poled PVDF-TrFE copolymer is obtained from *in situ* x-ray diffraction and quasielastic neutron scattering measurements at high temperatures. It is observed that the β-...

[Phys. Rev. B 96, 174103] Published Fri Nov 03, 2017

]]>With few systems of technological interest having been studied as extensively as elemental silicon, there currently exists a wide disparity between the number of predicted low-energy silicon polymorphs and those that have been experimentally realized as metastable at ambient conditions. We put forwa...

[Phys. Rev. B 96, 184101] Published Fri Nov 03, 2017

]]>Crystallization of liquid antimony has been studied at 600 K using six density functional/molecular dynamics simulations with up to 882 atoms and three scenarios: one completely disordered sample that did not crystallize even after 570 ps, four with fixed crystalline slab templates, and one with a f...

[Phys. Rev. B 96, 184102] Published Fri Nov 03, 2017

]]>The interlayer sliding behaviors of hexagonal boron nitride ($h$-BN) were investigated via a density functional theory approach with dispersion interaction included. It was found that the self-consistent screening effect (SCS) and the polarizability contractions had significant influences on London di...

[Phys. Rev. B 96, 174101] Published Wed Nov 01, 2017

]]>The ease with which domain walls (DWs) in ferroelectric materials can be *written* and *erased* provides a versatile way to dynamically modulate heat fluxes. In this Rapid Communication we evaluate the thermal boundary resistance (TBR) of ${180}^{\circ}$ DWs in the prototype ferroelectric perovskite ${\mathrm{PbTiO}}_{3}$ within ...

[Phys. Rev. B 96, 140101(R)] Published Tue Oct 31, 2017

]]>Water ice is a molecular solid whose behavior under compression reveals the interplay of covalent bonding in molecules and forces acting between them. This interplay determines high-pressure phase transitions, the elastic and plastic behavior of ${\mathrm{H}}_{2}\mathrm{O}$ ice, which are the properties needed for modeling ...

[Phys. Rev. B 96, 134122] Published Mon Oct 30, 2017

]]>The charge-transfer insulating perovskite oxides currently used as fuel cell electrolytes undergo, at high temperature, an oxidation reaction $\frac{1}{2}{\mathrm{O}}_{2}\left(\mathrm{g}\right)+{\mathrm{V}}_{\mathrm{O}}^{\u2022\u2022}\to {\mathrm{O}}_{\mathrm{O}}^{\mathrm{X}}+2{\mathrm{h}}^{\u2022}$, that produces oxygen-type holes. Understanding the nature and mobility of these oxygen-type holes is an important step to improve the pe...

[Phys. Rev. B 96, 134123] Published Mon Oct 30, 2017

]]>Monoclinic gallium oxide ($\beta \text{\u2212}\mathrm{G}{\mathrm{a}}_{2}{\mathrm{O}}_{3}$) has important applications in power devices and deep UV optoelectronic devices because of such novel properties as a wide band gap, high breakdown electric field, and a wide range of $n$-type doping conductivity. However, the intrinsic failure mechanisms of $\beta \text{\u2212}\mathrm{G}{\mathrm{a}}_{2}{\mathrm{O}}_{3}$ r...

[Phys. Rev. B 96, 144113] Published Mon Oct 30, 2017

]]>Group/subgroup structural phase transitions are exploited in a wide variety of technologies, including those that rely on shape-memory behavior and on transformation toughening. Here, we introduce an approach to identify symmetry-adapted strain and shuffle order parameters for any group/subgroup str...

[Phys. Rev. B 96, 134121] Published Fri Oct 27, 2017

]]>We study the effect of a tetragonal, symmetry-conserving epitaxial strain on the phase transition sequence and the onset of three symmetry-breaking modes in ${\mathrm{SrBi}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$ by first-principles calculations. The interplay of the strain variation of energy expansion coefficients results in an interesting p...

[Phys. Rev. B 96, 144112] Published Fri Oct 27, 2017

]]>The reaction of tantalum with molecular hydrogen was studied by x-ray diffraction in a diamond-anvil cell at room temperature and pressures from 1 to 41 GPa. At pressures up to 5.5 GPa, a substoichiometric tantalum monohydride with a distorted bcc structure was shown to be stable. Its hydrogen conte...

[Phys. Rev. B 96, 134120] Published Thu Oct 26, 2017

]]>Nanometer-scale ferroelectric vortex that is characterized by a curling polarization around a core is regarded as a new state of matter. The control of vortex chirality by homogeneous electric field is a key to the utilization of vortices in technological applications, but remains elusive since the toroidal moment of a ferroelectric vortex is conjugate to a curled electric field rather than to a homogeneous one. Here, the authors design free-standing nanodots with rational nanostructures and demonstrate using phase-field modelling that the chirality of the polarization vortex in such designed nanodots is deterministically switched by a homogeneous electric field.

[Phys. Rev. B 96, 134119] Published Wed Oct 25, 2017

]]>Spin behaviors on kagome lattices have received increased attention because of their exotic magnetic states. Here, we report magnetic ordering in the $S=2$ kagome antiferromagnet $\mathrm{MgF}{\mathrm{e}}_{3}{\left(\mathrm{OH}\right)}_{6}\mathrm{C}{\mathrm{l}}_{2}$. The compound has been synthesized by selectively replacing the magnetic ions in the triangular planes of its...

[Phys. Rev. B 96, 144111] Published Tue Oct 24, 2017

]]>We measure and analyze the statistics of nanoindentation pop-ins in a bulk metallic glass that has been annealed after being subjected to high pressure torsion. We argue that these pop-ins are avalanches of slip events. Larger slip avalanches are observed after annealing at higher temperatures. The ...

[Phys. Rev. B 96, 134117] Published Thu Oct 19, 2017

]]>With large specific and volumetric capacity, lithiated silicon is an excellent anode for lithium-ion batteries. Its application is challenged today, however, by the formation of an amorphous $a-{\text{Li}}_{x}\text{Si}$ phase associated with a large volume change that occurs at relatively low Li concentration and remain...

[Phys. Rev. B 96, 134118] Published Thu Oct 19, 2017

]]>Activating multiple symmetry modes and promoting a strong coupling between different modes by strain are indispensable to stabilize a polar ferroelectric (FE) phase from a nonpolar perovskite. Herein, through first-principles calculations, we propose an undiscovered and general avenue to engineering...

[Phys. Rev. B 96, 144110] Published Thu Oct 19, 2017

]]>A definition of the Grüneisen parameters for anisotropic materials is derived based on the response of phonon frequencies to uniaxial stress perturbations. This Grüneisen model relates the thermal expansion in a given direction (${\alpha}_{ii}$) to one element of the elastic compliance tensor, which corresponds...

[Phys. Rev. B 96, 134113] Published Wed Oct 18, 2017

]]>We report the dynamics of soft phonon modes and their role toward various structural transformations in Aurivillius materials by employing terahertz frequency-domain spectroscopy, atomic pair distribution function analysis, and first-principles calculations. We have chosen $\mathrm{B}{\mathrm{i}}_{4}\mathrm{T}{\mathrm{i}}_{3}{\mathrm{O}}_{12}$ as a model syste...

[Phys. Rev. B 96, 134114] Published Wed Oct 18, 2017

]]>We investigate the self-compensation mechanism in phosphorus-doped CdTe. The formation energies, charge transition levels, and defect states of several P-related point defects susceptible to cause self-compensation are addressed by first-principles calculations. Moreover, we assess the influence of ...

[Phys. Rev. B 96, 134115] Published Wed Oct 18, 2017

]]>We present results of electronic structure calculations of the bulk properties of CrAs. The crystalline structures of CrAs are investigated by the use of *ab initio* calculations with an unbiased swarm structural search under ambient and high pressure. Both the double helimagnetic and nonmagnetic phas...

[Phys. Rev. B 96, 134116] Published Wed Oct 18, 2017

]]>Recently, $\mathrm{Pb}\left(\mathrm{I}{\mathrm{n}}_{1/2}\mathrm{N}{\mathrm{b}}_{1/2}\right){\mathrm{O}}_{3}\text{\u2212}\mathrm{PbZr}{\mathrm{O}}_{3}\text{\u2212}\mathrm{Pb}\left(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}\right){\mathrm{O}}_{3}\text{\u2212}\mathrm{PbTi}{\mathrm{O}}_{3}$ (PIN-PZ-PMN-PT) relaxor single crystals were demonstrated to possess improved temperature-insensitive properties, which would be desirable for high-power device applications. The relaxor character associated with the development of local rand...

[Phys. Rev. B 96, 144109] Published Wed Oct 18, 2017

]]>Selenium is the only easily vitrified elementary substance. Numerous experimental studies of glassy Se ($g$-Se) at high pressures show a large spread in the data on the compressibility and electrical resistivity of $g$-Se. Furthermore, H. Liu *et al.* [Proc. Natl. Acad. Sci. USA **105**, 13229 (2008)] have ar...

[Phys. Rev. B 96, 134111] Published Tue Oct 17, 2017

]]>Bulk Au-Fe alloys separate into Au-based fcc and Fe-based bcc phases, but ${\mathrm{L}1}_{0}$ and ${\mathrm{L}1}_{2}$ orderings were reported in single-phase Au-Fe nanoparticles. Motivated by these observations, we study the structural and ordering energetics in this alloy by combining density functional theory (DFT) calculations ...

[Phys. Rev. B 96, 134109] Published Mon Oct 16, 2017

]]>We present *in situ* high-pressure synchrotron x-ray diffraction (XRD) and electrical transport measurements on quasi-one-dimensional single-crystal $\mathrm{Ti}{\mathrm{S}}_{3}$ up to 29.9–39.0 GPa in diamond-anvil cells, coupled with first-principles calculations. Counterintuitively, the conductive behavior of semiconductor...

[Phys. Rev. B 96, 134110] Published Mon Oct 16, 2017

]]>Scandium hydrides at high pressures have been investigated by using *ab initio* density functional calculations. Although the stable scandium hydride so far known to have the highest content rate of hydrogen is ${\mathrm{ScH}}_{3}$, other more hydrogen-rich compounds are found to be possible at high pressures. These ...

[Phys. Rev. B 96, 144108] Published Mon Oct 16, 2017

]]>Relaxor ferroelectric materials, such as $\mathrm{Pb}\left[{\left(\mathrm{M}{\mathrm{g}}_{0.33}\mathrm{N}{\mathrm{b}}_{0.67}\right)}_{1\text{\u2212}x}\mathrm{T}{\mathrm{i}}_{x}\right]{\mathrm{O}}_{3}$ (PMN-PT) with generic stoichiometry, undergo a ferroelectric-to-paraelectric phase transition as a function of temperature. The exact transition characterized by Curie temperature (${T}_{c}$) varies as a function of chemistry ($x$), i.e., th...

[Phys. Rev. B 96, 134108] Published Fri Oct 13, 2017

]]>A 1D anharmonic chain with a single impurity particle is used to study the vibrational energy localization. Numerical and asymptotic solutions for the symmetric anharmonic localized mode are both presented. The numerical results reveal that the energy localization strengthens with decreasing impurit...

[Phys. Rev. B 96, 144107] Published Fri Oct 13, 2017

]]>The spatiotemporal dynamics of the spin transition have been thoroughly investigated in single crystals of the mononuclear spin-crossover (SCO) complex $\left[\mathrm{Fe}\left(\mathrm{HB}\right(\mathrm{tz}{)}_{3}{)}_{2}\right]$ ($\mathrm{tz}=1,2$,4-triazol-1-yl) by optical microscopy. This compound exhibits an abrupt spin transition centered at 334 K with a narrow therm...

[Phys. Rev. B 96, 134106] Published Wed Oct 11, 2017

]]>Using the conventional macroscopic description of the bulk photovoltaic effect we analyze the light-induced currents and electric fields arising in the optical configuration with a continuous bottom electrode and a small circular top electrode. This scheme is relevant to recent experiments on the ti...

[Phys. Rev. B 96, 134107] Published Wed Oct 11, 2017

]]>We report a detailed single-crystal and powder neutron diffraction study of ${\mathrm{Co}}_{2}{\mathrm{TiO}}_{4}$ and ${\mathrm{Co}}_{2}{\mathrm{SnO}}_{4}$ between the temperature 1.6 and 80 K to probe the spin structure in the ground state. For both compounds the strongest magnetic intensity was observed for the (111)${}_{\text{M}}$ reflection due to ferrimagnetic orderi...

[Phys. Rev. B 96, 144104] Published Wed Oct 11, 2017

]]>Through high-pressure Raman spectroscopy and x-ray diffraction experiments, we have investigated the formation, stability field, and structure of hydrogen iodide (HI). Hydrogen iodide is synthesized by the reaction of molecular hydrogen and iodine at room temperature and at a pressure of 0.2 GPa. Up...

[Phys. Rev. B 96, 144105] Published Wed Oct 11, 2017

]]>Hexagonal boron nitride (hBN) is a wide-band-gap semiconductor with applications including gate insulation layers in graphene transistors, far-ultraviolet light emitting devices and as hydrogen storage media. Due to its complex microstructure, defects in hBN are challenging to identify. Here, we com...

[Phys. Rev. B 96, 144106] Published Wed Oct 11, 2017

]]>Negative thermal expansion coefficients ($\alpha $) are found in the fcc and cI16 (a distorted bcc structure) phases of sodium at pressures above 90 GPa from first principles. At room temperature, the most significant negative $\alpha $ of about $-4.5\times {10}^{-6}\phantom{\rule{4pt}{0ex}}{\mathrm{K}}^{-1}$ is predicted in fcc sodium at 120 GPa, which represents t...

[Phys. Rev. B 96, 134104] Published Tue Oct 10, 2017

]]>Monitoring structural changes in ferroelectric thin films during electric field induced polarization switching is important for a full microscopic understanding of the coupled motion of charges, atoms, and domain walls in ferroelectric nanostructures. We combine standard ferroelectric test sequences...

[Phys. Rev. B 96, 134105] Published Tue Oct 10, 2017

]]>Within the framework of a realistic multiband $p-d$ model, we derived an effective Hamiltonian to describe the exchange interaction effects near the spin crossover in magnetic Mott-Hubbard insulators under pressure. It is shown that the single-ion mechanism of spin crossover under the change in the cr...

[Phys. Rev. B 96, 134103] Published Mon Oct 09, 2017

]]>Controlling and manipulating the topological state represents an important topic in condensed matters for both fundamental researches and applications. In this work, we focus on the evolution of a real-space topological domain structure in hexagonal manganites driven by electric field, using the ana...

[Phys. Rev. B 96, 144103] Published Mon Oct 09, 2017

]]>By using the density functional theory plus $U$ (DFT+$U$) method and taking spin-orbit coupling into account, we investigate the electronic and phonon properties of ${\mathrm{Pu}}_{3}\mathrm{Ga}$. Most interestingly, we find that there is a significant phonon softening in the transverse acoustic branch at the $L$ point in the Bri...

[Phys. Rev. B 96, 134102] Published Wed Oct 04, 2017

]]>Guided elastic waves in homogeneous isotropic plates exhibit conical dispersion at zero wave number for discrete values of Poisson's ratio where accidental degeneracy between longitudinal and transverse thickness resonances occur. Waves excited at the coincidence frequency have the infinite phase ve...

[Phys. Rev. B 96, 144101] Published Wed Oct 04, 2017

]]>Hybrid quantum/classical techniques can flexibly couple *ab initio* simulations to an empirical or elastic medium to model materials systems that cannot be contained in small periodic supercells. However, due to electronic nonlocality, a total energy cannot be defined, meaning energy barriers cannot b...

[Phys. Rev. B 96, 144102] Published Wed Oct 04, 2017

]]>Using laser-generated shock waves, we have measured pressure, density, and temperature of LiH on the principal Hugoniot between 260 and 1100 GPa (2.6–11 Mbar) and on a second-shock Hugoniot up to 1400 GPa to near fivefold compression, extending the maximum pressure reached in non-nuclear experiments...

[Phys. Rev. B 96, 134101] Published Mon Oct 02, 2017

]]>Using the Landau-Ginzburg-Devonshire theory and one component approximation, we examined the conditions of the soft acoustic phonon mode (**A**-mode) appearance in a ferroelectric (FE) depending on the magnitude of the flexoelectric coefficient $f$ and temperature $T$. If the flexocoefficient $f$ is equal to ...

[Phys. Rev. B 96, 094111] Published Fri Sep 29, 2017

]]>Boron nitride polymorphs hold great promise for integration into electronic and optoelectronic devices requiring ultrawide band gaps. We use first-principles calculations to examine the prospects for $p$-type doping of hexagonal ($h-\mathrm{BN}$), wurtzite ($wz-\mathrm{BN}$), and cubic ($c-\mathrm{BN}$) boron nitride. Group-IV elemen...

[Phys. Rev. B 96, 100102(R)] Published Fri Sep 29, 2017

]]>The local atomic geometries in ${\mathrm{Ba}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{TiO}}_{3}$ thin films grown on MgO(001) substrates have been determined by Ti $1s$ near-edge x-ray-absorption fine-structure measurements and density-functional-theory calculations. The accuracy of the atomic geometries predicted by density-functional theory is demon...

[Phys. Rev. B 96, 104111] Published Thu Sep 28, 2017

]]>Solid ${\mathrm{NH}}_{4}\mathrm{F}$ displays intriguing parallels with ice despite its apparently ionic character. Here we investigate its phase diagram in low-temperature and high-pressure regions using Raman spectroscopy, x-ray diffraction, and *ab initio* structure search calculations. We focus on the high-pressure cubic ...

[Phys. Rev. B 96, 094110] Published Mon Sep 25, 2017

]]>Time-space modulated media are realized by periodically modulating parameters of the media in both time and space. In this paper, we study frequency conversion induced by time-space modulated media. Two types of frequency conversion are theoretically and numerically demonstrated; their underlying me...

[Phys. Rev. B 96, 104110] Published Mon Sep 25, 2017

]]>Strain-phonon coupling, in terms of the shift in phonon frequencies under biaxial strain, is studied by density functional theory calculations for 20 perovskite oxides strained in their (111) and (001) planes. While the strain-phonon coupling under (001) strain follows the established, intuitive tre...

[Phys. Rev. B 96, 094109] Published Wed Sep 20, 2017

]]>An incommensurate phase refers to a solid state in which the period of a superstructure is incommensurable with its primitive unit cell. It was recently shown that an incommensurate phase, which displays a single chiral modulation of six domain variants, could be induced by applying an in-plane stra...

[Phys. Rev. B 96, 104109] Published Wed Sep 20, 2017

]]>High-temperature, high-dose, neutron irradiation of W results in the formation of Re-rich clusters at concentrations one order of magnitude lower than the thermodynamic solubility limit. These clusters may eventually transform into brittle W-Re intermetallic phases, which can lead to high levels of ...

[Phys. Rev. B 96, 094108] Published Mon Sep 18, 2017

]]>A density functional theory study of atomic defects and dopants in ternary Z-phase transition-metal nitrides $\mathrm{Cr}M\mathrm{N}$ with $M=\mathrm{V}$, Nb, or Ta is presented. Various defect formation energies of native point defects and of substitutional atoms of other metal elements which are abundant in the steel as well ar...

[Phys. Rev. B 96, 104107] Published Mon Sep 18, 2017

]]>Kinetic Monte Carlo simulations have been performed to investigate the evolution of ordered domains in model alloys under irradiation. The alloys investigated were equiatomic binary alloys on a simple square lattice with first and second nearest-neighbor interactions, chosen so that a $2\times 2$ ordered st...

[Phys. Rev. B 96, 104108] Published Mon Sep 18, 2017

]]>Small system sizes are a well-known source of error in density functional theory (DFT) calculations, yet computational constraints frequently dictate the use of small supercells, often as small as 96 atoms in oxides and compound semiconductors. In ionic compounds, electrostatic finite-size effects h...

[Phys. Rev. B 96, 094107] Published Fri Sep 15, 2017

]]>Our detailed temperature-dependent synchrotron powder x-ray diffraction studies along with first-principles density-functional-theory-based calculations enable us to shed light on the origin of ferroelectricity in ${\mathrm{GdCrO}}_{3}$. The actual lattice symmetry is found to be the noncentrosymmetric orthorhombic...

[Phys. Rev. B 96, 104106] Published Tue Sep 12, 2017

]]>Topological phononic states, which facilitate unique acoustic transport around defects and disorders, have significantly revolutionized our scientific cognition of acoustic systems. Here, by introducing a zone folding mechanism, we realize the topological phase transition in a double Dirac cone of t...

[Phys. Rev. B 96, 094106] Published Mon Sep 11, 2017

]]>The diffusivities of substitutional impurity elements in iron have been computed with *ab inito* electronic density functional techniques, using exchange-correlation functional PW91. Excess entropies and the attempt frequency for a jump were determined by calculating phonon frequencies in the harmonic...

[Phys. Rev. B 96, 094105] Published Thu Sep 07, 2017

]]>The authors demonstrate room-temperature multiferroic (ferroelectric-ferromagnetic) behavior in lead titanate, in which about 30% of the titanium is substituted by palladium. Palladium is an unusual element with an instability to ferromagnetism under some special conditions. Typically, it has not been easy to incorporate it into perovskite oxides – the most common structure for ferroelectric device materials. Although palladium is expensive, commercial devices like ferroelectric memories often use very thin films, for which the added cost of palladium is negligible. Thus, the present study combines basic new physics of the first multiferroic palladium compounds with potential commercial devices.

[Phys. Rev. B 96, 104104] Published Thu Sep 07, 2017

]]>The spinel $\mathrm{CoC}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$ (CCO) is one of the few bulk multiferroics with net magnetic moment. However, studies on the properties of CCO thin films are scarce. Here, we investigate the interplay between microstructure and magnetism of a series of CCO epitaxial thin films by means of x-ray diffraction, magn...

[Phys. Rev. B 96, 104105] Published Thu Sep 07, 2017

]]>Shear banding is a nucleation-controlled process in metallic glasses (MGs) involving multiple temporal-spatial scales, which hinders a concrete understanding of its structural origin down to the atomic scale. Here, inspired by the morphology of composite materials, we propose a different perspective...

[Phys. Rev. B 96, 094103] Published Wed Sep 06, 2017

]]>We report high-pressure Raman experiments of black phosphorus up to 24 GPa. The linewidths of first-order Raman modes ${A}_{g}^{1},{B}_{2g}$, and ${A}_{g}^{2}$ of the orthorhombic phase show a minimum at 1.1 GPa. Our first-principles density functional analysis reveals that this is associated with the anomalies in electron...

[Phys. Rev. B 96, 094104] Published Wed Sep 06, 2017

]]>Density functional theory in principle predicts correct ground-state properties for all materials. However, the rocksalt structure of MnO has been obtained only by the high-level random phase approximation and diffusion Monte Carlo (DMC). Here, we propose and test for MnO, FeO, CoO, and NiO that a s...

[Phys. Rev. B 96, 100101(R)] Published Wed Sep 06, 2017

]]>We explore the elastic, dielectric, piezoelectric, and flexoelectric phenomenological coefficients as functions of microscopic model parameters such as ionic positions and spring constants in the two-dimensional square-lattice model with rocksalt-type ionic arrangement. Monte Carlo simulation reveal...

[Phys. Rev. B 96, 104102] Published Wed Sep 06, 2017

]]>The $\mathrm{P}{\mathrm{b}}_{\mathrm{I}}$ antisite was reported to be a possible deep-level recombination-center defect in $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Pb}{\mathrm{I}}_{3}$ solar cells with a concentration higher than ${10}^{15}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{-3}$ under I-poor conditions. However, whether it is really an effective nonradiative recombination center and limits the photovoltaic efficiency depen...

[Phys. Rev. B 96, 104103] Published Wed Sep 06, 2017

]]>The ferroelectric to paraelectric phase transition of multiferroic ${\mathrm{CaMnTi}}_{2}{\mathrm{O}}_{6}$ has been investigated at high pressures and ambient temperature by second-harmonic generation (SHG), Raman spectroscopy, and powder and single-crystal x-ray diffraction. We have found that ${\mathrm{CaMnTi}}_{2}{\mathrm{O}}_{6}$ undergoes a pressure-ind...

[Phys. Rev. B 96, 094101] Published Tue Sep 05, 2017

]]>High-throughput first-principles calculations based on density functional theory (DFT) are a powerful tool in data-oriented materials research. The choice of approximation to the exchange-correlation functional is crucial as it strongly affects the accuracy of DFT calculations. This study compares p...

[Phys. Rev. B 96, 094102] Published Tue Sep 05, 2017

]]>The exceptional ability of carbon to form ${\mathit{sp}}^{2}$ and ${\mathit{sp}}^{3}$ bonding states leads to a great structural and chemical diversity of carbon-bearing phases at nonambient conditions. Here we use laser-heated diamond-anvil cells combined with synchrotron x-ray diffraction, Raman spectroscopy, and first-principle...

[Phys. Rev. B 96, 104101] Published Fri Sep 01, 2017

]]>A continuum/atomistic approach for predicting lattice instability during crystal-crystal phase transformations (PTs) is developed for the general loading with an arbitrary stress tensor and large strains. It is based on a synergistic combination of the generalized Landau-type theory for PTs and mole...

[Phys. Rev. B 96, 054118] Published Tue Aug 29, 2017

]]>The phonon anharmonicity in Se-doped $\mathrm{S}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{e}}_{3}$ system is probed both macroscopically and microscopically using temperature-dependent synchrotron powder diffraction, Raman spectroscopic studies, and heat-capacity measurements. Gruneisen parameter (${\gamma}_{\mathrm{G}}$) is calculated to explain anharmonicity in the polycr...

[Phys. Rev. B 96, 064116] Published Tue Aug 29, 2017

]]>The phase transition evolution for ${\left[{\mathrm{KNbO}}_{3}\right]}_{1-x}{\left[{\mathrm{BaNi}}_{1/2}{\mathrm{Nb}}_{1/2}{\mathrm{O}}_{3-\delta}\right]}_{x}\phantom{\rule{0.16em}{0ex}}(x=0,0.1)$ is determined via complementary dielectric permittivity and Raman-scattering measurements. Raman scattering by optical phonons over the range of 100–$1000{\mathrm{cm}}^{-1}$ for 83 K $<T<873$ K reveals six discernible zone-center optical ...

[Phys. Rev. B 96, 054117] Published Mon Aug 28, 2017

]]>Ferroelectric perovskite oxides possess a large electrocaloric (EC) effect, but usually at high temperatures near the ferroelectric/paraelectric phase transition temperature, which limits their potential application as next-generation solid-state cooling devices. We use classical molecular dynamics ...

[Phys. Rev. B 96, 054116] Published Thu Aug 24, 2017

]]>The nucleation and growth properties of domains of molecules of the same state in open boundary three-dimensional (3D) spin-crossover systems of various shapes are discussed within the framework of the mechanoelastic model. The molecules are situated on face-centered-cubic lattices and are linked by...

[Phys. Rev. B 96, 064115] Published Thu Aug 24, 2017

]]>We present a rigorous procedure for evaluating the photoelastic coefficients of a layered medium in which the periodicity is smaller than the wavelengths of all optical and acoustic fields. Analytical expressions are given for the coefficients of a composite material comprising thin layers of optica...

[Phys. Rev. B 96, 064114] Published Wed Aug 23, 2017

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