The potential of quarternary wurtzite ${\mathrm{TM}}_{x/2}{\mathrm{M}}_{x/2}{\mathrm{Al}}_{1-x}\mathrm{N}$ ($\mathrm{TM}=\text{Ti}$, Zr, Hf; $\mathrm{M}=\text{Mg}$, Ca, Zn) alloys for piezoelectric applications is investigated using first-principles calculations. All considered alloys show increased piezoelectric response compared to pure AlN, and competing with the best ternary system …

[Phys. Rev. B 92, 174119] Published Wed Nov 25, 2015

]]>The elastic energy functional of a system of discrete dislocation lines is well known from dislocation theory. In this paper, we demonstrate how the discrete functional can be used to systematically derive approximations which express the elastic energy in terms of dislocation densitylike variables …

[Phys. Rev. B 92, 174120] Published Wed Nov 25, 2015

]]>We report calculations of phonon dispersions of iron (Fe) at its $\gamma -\delta $ phase transition using a self-consistent *ab initio* lattice dynamical method in conjunction with an effective magnetic force approach via the antiferromagnetic approximation. Our results show that anharmonic phonon-phonon interactio…

[Phys. Rev. B 92, 184110] Published Tue Nov 24, 2015

]]>Density functional theory (DFT) calculations of 58 liquid elements at their triple point show that most metals exhibit near proportionality between the thermal fluctuations of the virial and the potential energy in the isochoric ensemble. This demonstrates a general “hidden” scale invariance of meta…

[Phys. Rev. B 92, 174116] Published Mon Nov 23, 2015

]]>A first-principles study of the $L{1}_{2}\phantom{\rule{4pt}{0ex}}{\text{Co}}_{3}(\text{Al},\text{W})$ phase was performed to assess phase stability at elevated temperature. Configurational degrees of freedom were treated with a cluster expansion and Monte Carlo simulations, while contributions to the free energy from vibrational excitations were determine…

[Phys. Rev. B 92, 174117] Published Mon Nov 23, 2015

]]>The thermodynamic compensation law describing an empirical linear relationship between activation enthalpy and activation entropy has seldom been validated for amorphous solids. Here molecular dynamics simulations reveal a well-defined enthalpy-entropy compensation rule in a metallic glass (MG) over…

[Phys. Rev. B 92, 174118] Published Mon Nov 23, 2015

]]>Molecular-dynamics simulations combined with a two-temperature model are used to study laser ablation in ${\text{Cu}}_{x}{\text{Zr}}_{1-x}$ $\left(x=0.33,0.50,0.67\right)$ metallic glasses as well as crystalline ${\text{CuZr}}_{2}$ in the ${\text{C11}}_{b}$ $\left({\text{MoSi}}_{2}\right)$ structure. Ablation thresholds are found to be $430\pm 10,450\pm 10,510\pm 10$, and $470\pm 10$ ${\mathrm{J}/\mathrm{m}}_{2}$ for a-${\text{Cu}}_{2}\text{Zr}$, a-C…

[Phys. Rev. B 92, 184108] Published Mon Nov 23, 2015

]]>This paper introduces a phase-field crystal (PFC) approach that couples the atomic-scale PFC density field to order parameters describing ferromagnetic and ferroelectric ordering, as well to a solute impurity field. This model extends the magnetic PFC model introduced by Faghihi *et al.* [N. Faghihi, …

[Phys. Rev. B 92, 184109] Published Mon Nov 23, 2015

]]>Molybdenum (Mo) is a body-centered-cubic (bcc) transition metal that has widespread technological applications. Although the bcc transition elements are used as test cases for understanding the behavior of metals under extreme conditions, the melting curves and phase transitions of these elements ha…

[Phys. Rev. B 92, 174114] Published Fri Nov 20, 2015

]]>A full understanding of the basic processes of grain boundary migration is a fundamental prerequisite for predictive models of microstructural evolution in polycrystalline materials in processing and in service. In a detailed study of the kinetics of a $\left[111\right]\mathrm{\Sigma}7$ symmetric tilt boundary, we have previ…

[Phys. Rev. B 92, 174115] Published Fri Nov 20, 2015

]]>The stress-induced martensitic transition in a Cu-Zn-Al shape memory alloy has been studied under three different driving conditions by using (i) a hard driving device which imposes a displacement rate on the sample heads, (ii) a soft driving device which imposes a loading rate on the sample, and (i…

[Phys. Rev. B 92, 184107] Published Fri Nov 20, 2015

]]>The structure and superfluid response of nanoscale size ${}^{4}\mathrm{He}$ clusters enclosed in spherical cavities are studied by computer simulations. The curved surface causes the formation of well-defined concentric shells, thus imparting to the system a very different structure from that of freestanding cluste…

[Phys. Rev. B 92, 174112] Published Thu Nov 19, 2015

]]>We measured the absolute lengths of three single-crystal silicon samples by means of an imaging Twyman-Green interferometer in the temperature range from 7 K to 293 K with uncertainties of about 1 nm. From these measurements we extracted the coefficient of thermal expansion with uncertainties on the…

[Phys. Rev. B 92, 174113] Published Thu Nov 19, 2015

]]>We have studied the temperature induced $0-\pi $ thermodynamic transition in Nb/PdNi/Nb superconductor/ferromagnetic/superconductor (SFS) heterostructures by microwave measurements of the superfluid density. We have observed a shift in the transition temperature with the ageing of the heterostructures, s…

[Phys. Rev. B 92, 184106] Published Thu Nov 19, 2015

]]>We derive a general theory of effective properties in metasolids based on phononic crystals with low frequency resonances. We demonstrate that in general these structures need to be described by means of a frequency-dependent and nonlocal anisotropic mass density, stiffness tensor and a third-rank c…

[Phys. Rev. B 92, 174110] Published Tue Nov 17, 2015

]]>The equilibrium structure and functional properties exhibited by brownmillerite oxides, a family of perovskite-derived structures with alternating layers of $B{\mathrm{O}}_{6}$ octahedra and $B{\mathrm{O}}_{4}$ tetrahedra, viz., ordered arrangements of oxygen vacancies, is dependent on a variety of competing crystal-chemistry fact…

[Phys. Rev. B 92, 174111] Published Tue Nov 17, 2015

]]>We present a multiphase-field theory for describing pattern formation in multidomain and/or multicomponent systems. The construction of the free energy functional and the dynamic equations is based on criteria that ensure mathematical and physical consistency. We first analyze previous multiphase-fi…

[Phys. Rev. B 92, 184105] Published Tue Nov 17, 2015

]]>Ultrafast laser irradiation can trigger anisotropically structured nanoscaled gratinglike arrangements of matter, the laser-induced periodic surface structures (LIPSSs). We demonstrate here that the formation of LIPSS is intrinsically related to the coherence of the laser field. Employing several te…

[Phys. Rev. B 92, 174109] Published Fri Nov 13, 2015

]]>Using first-principles evolutionary simulations, we have systematically investigated phase stability in the Hf-O system at pressure up to 120 GPa. New compounds ${\mathrm{Hf}}_{5}{\mathrm{O}}_{2},{\mathrm{Hf}}_{3}{\mathrm{O}}_{2}$, HfO, and ${\mathrm{HfO}}_{3}$ are discovered to be thermodynamically stable at certain pressure ranges. Two new high-pressure phases are found…

[Phys. Rev. B 92, 184104] Published Fri Nov 13, 2015

]]>By means of *ab initio* molecular dynamics calculations, the thermal evolution of vibrational properties in $\alpha $-U is studied at low temperature. The phase transition undergone by this material around 50 K was previously studied extensively using *ab initio* calculations in the framework of the linear resp…

[Phys. Rev. B 92, 174108] Published Wed Nov 11, 2015

]]>The melting curve of osmium up to a pressure $P$ of 500 GPa is obtained from an extensive suite of *ab initio* quantum molecular dynamics (QMD) simulations using the Z method. The *ab initio* $P=0$ melting point of Os is $3370\pm 75$ K; this range encompasses all of the available data in the literature and corro…

[Phys. Rev. B 92, 174105] Published Mon Nov 09, 2015

]]>Recent progress of high-pressure technology enables the synthesis of novel metal borides with diverse compositions and interesting properties. A precise characterization of these borides, however, is sometimes hindered by multiphase intergrowth and grain-size limitation in the synthesis process. Her…

[Phys. Rev. B 92, 174106] Published Mon Nov 09, 2015

]]>The properties of the interface between solid and melt are key to solidification and melting, as the interfacial free energy introduces a kinetic barrier to phase transitions. This makes solidification happen below the melting temperature, in out-of-equilibrium conditions at which the interfacial fr…

[Phys. Rev. B 92, 180102(R)] Published Mon Nov 09, 2015

]]>The isothermal compressibility of a general crystal is analyzed within classical density functional theory. Our approach can be used for homogeneous and unstrained crystals containing an arbitrarily high density of local defects. We start by coarse-graining the microscopic particle density and then …

[Phys. Rev. B 92, 184103] Published Mon Nov 09, 2015

]]>Previous studies have indicated that the figure of merit ($\mathit{ZT}$) of half-Heusler (HH) alloys with composition $M\mathrm{NiSn}$ ($M\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}\mathrm{Ti}$, Zr, or Hf) is greatly enhanced when the alloys contain a nano-scale full-Heusler (FH) $\mathrm{MN}{\mathrm{i}}_{2}\mathrm{Sn}$ second phase. However, the formation mechanism of the FHnanostructures in the HH matrix…

[Phys. Rev. B 92, 174102] Published Fri Nov 06, 2015

]]>Microscopic polar clusters can play an important role in the phase transition of ferroelectric perovskite oxides such as $\mathrm{BaTi}{\mathrm{O}}_{3}$, which have shown coexistence of both displacive and order-disorder dynamics, although their topological and dynamical characteristics are yet to be clarified. Here, we rep…

[Phys. Rev. B 92, 174103] Published Fri Nov 06, 2015

]]>Subpicosecond double-pulse laser ablation of metals is simulated using a hybrid model that combines classical molecular dynamics and an energy equation for free electrons. The key advantage of our model is the usage of the Helmholtz wave equation for the description of the laser energy absorption. A…

[Phys. Rev. B 92, 174104] Published Fri Nov 06, 2015

]]>Martensites, which are the product of diffusionless phase transitions, can form phases with small periodic modulations of crystalline atomic lattice positions. Experiments have shown both that the modulation function is smooth and that when more than one modulation is present they can be incommensurate. These observations have appeared to be inconsistent with nanotwinning models. Here the authors show theoretically that in the case of the ferromagnetic shape memory alloy NiMnGa, the presence of two competing mechanisms favoring different commensurate periodic structures, a result of the interaction between different minima in the energy landscape, can lead to effective smooth incommensurate modulations consistent with nanotwinning models.

[Phys. Rev. B 92, 180101(R)] Published Fri Nov 06, 2015

]]>A first-principles based approach to calculating self-diffusion rates in bcc Fe is discussed with particular focus on the magnetic free energy associated with diffusion activation. First, the enthalpies and entropies of vacancy formation and migration in ferromagnetic bcc Fe are calculated from stan…

[Phys. Rev. B 92, 184102] Published Fri Nov 06, 2015

]]>Phase transformations induced in the cubic C-type lanthanide sesquioxides, ${\mathrm{Ln}}_{2}{\mathrm{O}}_{3}$ (Ln = Sm, Gd, Ho, Tm, and Lu), by dense electronic excitation are investigated. The structural modifications resulting from exposure to beams of 185 MeV Xe and 2246 MeV Au ions are characterized using synchrotron x-ray …

[Phys. Rev. B 92, 174101] Published Tue Nov 03, 2015

]]>We demonstrate that use of the field effect enables tuning of the effective optical parameters of a layered hyperbolic metamaterial at optical frequencies. Field-effect gating electrically modulates the permittivity in transparent conductive oxides via changes in the carrier density. These permittiv…

[Phys. Rev. B 92, 184101] Published Mon Nov 02, 2015

]]>The effect of electronic dispersion over a wide variety of ${\mathrm{SiO}}_{2}$ polymorphs (faujasite, ferrierite, $\alpha $-cristobalite, $\alpha $-quartz, coesite, and stishovite) is investigated using state-of-the-art density functional theory. Different functionals and dispersion correction schemes are compared, ranging from t…

[Phys. Rev. B 92, 144111] Published Fri Oct 30, 2015

]]>We report on molecular dynamics studies of phonon (lattice vibrations) transport in bilayer silicon thin films stuck together via van der Waals interactions. Results indicate that for bilayer thin films with an atomically smooth interface, the in-plane thermal conductivity of the bilayer films is th…

[Phys. Rev. B 92, 134113] Published Thu Oct 29, 2015

]]>We have discovered stoichiometric LiB with hexagonal boron layers by compressing known ${\mathrm{LiB}}_{0.9}$ with linear boron chains. The $sp$ to $s{p}^{2}$ rebonding occurred at *room* temperature and pressures above 21 GPa. The study was motivated by a long-standing prediction that LiB in the stable layered configuration …

[Phys. Rev. B 92, 144110] Published Thu Oct 29, 2015

]]>*In situ* high-pressure Raman spectroscopy and *ab initio* calculations are carried out to investigate the phase stability and the thermal expansion behavior of ${\mathrm{H}}_{3}\left[\mathrm{Co}(\mathrm{CN}{)}_{6}\right]$. Raman studies at high pressures in a diamond anvil cell identify soft phonons and phase instability at 2.3 GPa. Evidence of pressu…

[Phys. Rev. B 92, 134112] Published Mon Oct 26, 2015

]]>Recent extended x-ray absorption fine structure (EXAFS) studies suggest that in skutterudites, the nearly square rings (such as ${\mathrm{As}}_{4}$ in ${\mathrm{CeFe}}_{4}{\mathrm{As}}_{12}$) are quite rigid and may vibrate with low-energy modes in one direction, similar to “rattler” atom vibrations. That work suggests that the motions of the s…

[Phys. Rev. B 92, 134111] Published Wed Oct 21, 2015

]]>Despite the long history, so far there is no general theoretical framework for calculating the acoustic emission spectrum accompanying any plastic deformation. We set up a discrete wave equation with plastic strain rate as a source term and include the Rayleigh-dissipation function to represent diss…

[Phys. Rev. B 92, 144109] Published Tue Oct 20, 2015

]]>The rearrangement of a material's electron density during laser irradiation leads to modified nonthermal forces on the atoms that may lead to coherent atomic motions and structural phase transformation on very short time scales. We present *ab initio* molecular dynamics simulations of a martensitic so…

[Phys. Rev. B 92, 134110] Published Thu Oct 15, 2015

]]>Phase transitions in nickel-titanium shape-memory alloys are investigated by means of atomistic simulations. A second nearest-neighbor modified embedded-atom method interatomic potential for the binary nickel-titanium system is determined by improving the unary descriptions of pure nickel and pure t…

[Phys. Rev. B 92, 134107] Published Wed Oct 14, 2015

]]>In this work we present an alternative way to look at electron diffraction in a transmission electron microscope. Instead of writing the scattering amplitude in Fourier space as a set of plane waves, we use the cylindrical Fourier transform to describe the scattering amplitude in a basis of orbital …

[Phys. Rev. B 92, 134108] Published Wed Oct 14, 2015

]]>Ferromagnetic shape memory alloys (FSMAs) have shown great potential as active components in next generation smart devices due to their exceptionally large magnetic-field-induced strains and fast response times. During application of magnetic fields in FSMAs, as is common in several magnetoelastic s…

[Phys. Rev. B 92, 134109] Published Wed Oct 14, 2015

]]>The authors revisited the Mollwo–Ivey relation of $F$ centers in alkali halide crystals, a prototypical color center, based on post-density-functional-theory and post-Hartree-Fock methods. In contrast to earlier interpretations, which stress the importance of the Madelung potential, they find ion-size effects to be the predominant mechanism. These determine the shape of the defect-electron wave function and are responsible for the fractional Mollwo–Ivey exponent of 1.8.

[Phys. Rev. B 92, 144107] Published Wed Oct 14, 2015

]]>Singly ionized oxygen vacancies are produced in $\mathrm{LiAl}{\mathrm{O}}_{2}$ crystals by direct displacement events during a neutron irradiation. These vacancies, with one trapped electron, are referred to as ${\mathrm{V}}_{\mathrm{O}}^{+}$ centers. They are identified and characterized using electron paramagnetic resonance (EPR) and optical absorp…

[Phys. Rev. B 92, 144108] Published Wed Oct 14, 2015

]]>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

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