The strength of a material can be altered by temperature, pressure, grain size, and orientation distributions. At the microscale, neighboring grains often play important roles in the elastic and plastic deformation process. By applying high pressure to a mixture of germanium and gold powder in the v…

[Phys. Rev. B 94, 144104] Published Fri Oct 21, 2016

]]>We present *ab initio* results for linker decorations in Mg-MOF74, i.e., attaching various metals $\mathcal{M}=\text{Li}$, Na, K, Sc, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Pd, Ag, and Pt near the ring of the linker, creating new strong adsorption sites and thus maximizing small-molecule uptake. We find that in most cases these de…

[Phys. Rev. B 94, 144105] Published Fri Oct 21, 2016

]]>We report a high-pressure study of monoclinic monazite-type $\mathrm{SrCr}{\mathrm{O}}_{4}$ up to 26 GPa. Therein we combined x-ray diffraction, Raman, and optical-absorption measurements with *ab initio* calculations, to find a pressure-induced structural phase transition of $\mathrm{SrCr}{\mathrm{O}}_{4}$ near 8–9 GPa. Evidence of a second phase tr…

[Phys. Rev. B 94, 134108] Published Thu Oct 20, 2016

]]>We study the dynamics of quantum three-level systems due to fast fluctuations of their environment (white noise). As an example, we model the decoherence and dephasing of nitrogen-vacancy (NV) centers in diamond that are positioned near a surface that gives rise to quickly fluctuating magnetic field…

[Phys. Rev. B 94, 134107] Published Wed Oct 19, 2016

]]>A system driven in the vicinity of its critical point by varying a relevant field in an arbitrary function of time is a generic system that possesses a long relaxation time compared with the driving time scale and thus represents a large class of nonequilibrium systems. For such a manifestly nonline…

[Phys. Rev. B 94, 144103] Published Wed Oct 19, 2016

]]>We investigate phase separation including elastic coherency effects in the bulk and at surfaces and find a reduction of the solubility limit in the presence of free surfaces. This mechanism favors phase separation near free surfaces even in the absence of external stresses. We apply the theory to hy…

[Phys. Rev. B 94, 134106] Published Tue Oct 18, 2016

]]>Three extensive density functional/molecular dynamics simulations of the crystallization of amorphous ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$ (460 atoms) [Phys. Rev. B **90**, 184109 (2014)] have been completed with simulation times of up to 8.2 ns. Together with the results of earlier simulations with and without a crystallite seed…

[Phys. Rev. B 94, 134105] Published Mon Oct 17, 2016

]]>Thorium and its compounds have received considerable attention in recent years due to the renewed interest in developing the thorium fuel cycle as an alternative nuclear energy technology. There is pressing current need to explore the physical properties essential to the fundamental understanding an…

[Phys. Rev. B 94, 134104] Published Fri Oct 07, 2016

]]>Precipitation of anion nanocrystals (NCs) in initially stoichiometric II-VI crystals under hydrostatic pressure and light exposure is explored by Raman spectroscopy, and the mechanism for this effect is analyzed by model calculations. ZnSe, ZnTe, and CdSe crystals are studied in bulk and/or epitaxia…

[Phys. Rev. B 94, 134102] Published Thu Oct 06, 2016

]]>Strongly scattering elastic media, such as consolidated granular materials, respond to ultrasonic pulse excitations with a long response signal with peculiar properties. The portion of the signal at late times, termed coda, is due to multiple scattering. It contains information about the elastic pro…

[Phys. Rev. B 94, 134103] Published Tue Oct 04, 2016

]]>A hexagonal structure of solid molecular hydrogen with $P{6}_{1}22$ symmetry is calculated to be more stable below about 200 GPa than the monoclinic $C2/c$ structure identified previously as the best candidate for phase III. We find that the effects of nuclear quantum and thermal vibrations play a central ro…

[Phys. Rev. B 94, 134101] Published Mon Oct 03, 2016

]]>We have performed density functional theory (DFT) based calculations for aluminum in extreme conditions of both pressure and temperature, up to five times compressed ambient density, and over 1 000 000 K in temperature. In order to cover such a domain, DFT methods including phonon calculations, quan…

[Phys. Rev. B 94, 144101] Published Mon Oct 03, 2016

]]>A salient feature of cyclically driven first-order phase transformations in crystals is their scale-free avalanche dynamics. This behavior has been linked to the presence of a classical critical point but the mechanism leading to criticality without extrinsic tuning remains unexplained. Here we show…

[Phys. Rev. B 94, 144102] Published Mon Oct 03, 2016

]]>In electromagnetism, acoustics, and quantum mechanics, scattering problems can routinely be solved numerically by virtue of perfectly matched layers (PMLs) at simulation domain boundaries. Unfortunately, the same has not been possible for general elastodynamic wave problems in continuum mechanics. I…

[Phys. Rev. B 94, 100105(R)] Published Fri Sep 30, 2016

]]>The influence of defect dipoles on the electrocaloric effect (ECE) in acceptor doped ${\mathrm{BaTiO}}_{3}$ is studied by means of lattice-based Monte-Carlo simulations using a Ginzburg-Landau type effective Hamiltonian. Oxygen vacancy-acceptor associates are described by fixed local dipoles with orientation parall…

[Phys. Rev. B 94, 094113] Published Thu Sep 29, 2016

]]>Reversible polymorphism of monolayer transition-metal dichalcogenides (TMDC) has currently attracted much attention from both academic and applied perspectives. Of special interest is ${\mathrm{MoTe}}_{2}$, where the stable semiconducting $2H$ and metastable (semi)metallic $1{T}^{\prime}$ phases have a rather small energy differ…

[Phys. Rev. B 94, 094114] Published Thu Sep 29, 2016

]]>An improved thermodynamic cycle is validated in ferroelectric single crystals, where the cooling effect of an electrocaloric refrigerant is enhanced by applying a reversed electric field. In contrast to the conventional adiabatic heating or cooling by on-off cycles of the external electric field, ap…

[Phys. Rev. B 94, 100104(R)] Published Thu Sep 29, 2016

]]>The general method for the calculation of $n\mathrm{th}$ ($n\ge 2$) order elastic constants of the loaded crystal is given in the framework of the nonlinear elasticity theory. For the crystals of cubic symmetry under hydrostatic compression, the two schemes of calculation of the elastic constants of second, third, …

[Phys. Rev. B 94, 104114] Published Thu Sep 29, 2016

]]>The phase diagram of iridium is investigated using the Z methodology. The Z methodology is a technique for phase diagram studies that combines the direct Z method for the computation of melting curves and the inverse Z method for the calculation of solid-solid phase boundaries. In the direct Z metho…

[Phys. Rev. B 94, 094112] Published Wed Sep 28, 2016

]]>We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor ${\left({\mathrm{NbSe}}_{4}\right)}_{3}\mathrm{I}$ by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a well-documented pseudo-Jahn-Teller ferrodistortive structural transition at ${T}_{C}=274$ K, wh…

[Phys. Rev. B 94, 104113] Published Wed Sep 28, 2016

]]>We report on a comprehensive first-principles study of phase stability in the Ni-Al binary, both at zero Kelvin and at finite temperature. First-principles density functional theory calculations of the energies of enumerated orderings on fcc and the sublattices of B2 not only predict the stability o…

[Phys. Rev. B 94, 094111] Published Tue Sep 27, 2016

]]>Despite its fundamental importance in condensed matter physics and geophysical implications, establishing the systematic and direct link between the pressure-induced structural changes in crystalline and noncrystalline low-$z$ oxides and their corresponding evolution in O $K$-edge core-electron excitati…

[Phys. Rev. B 94, 094110] Published Mon Sep 26, 2016

]]>Ferroelectric vortex domains are of significant interest due to their rich physics and potential applications. Here, we propose the crystallographic, strain, and electric conditions for spontaneous vortex domains and study the influence of oxygen octahedral tilt on vortex wall orientations. Using 10…

[Phys. Rev. B 94, 100103(R)] Published Mon Sep 26, 2016

]]>The high-pressure structural and elastic properties of ${\mathrm{MgCO}}_{3},{\mathrm{CaCO}}_{3}$, and $\mathrm{MgCa}{\left({\mathrm{CO}}_{3}\right)}_{2}$ have been investigated with density functional theory. By computing the isotropic elastic constants, we found that the bulk and shear acoustic wave velocities are smaller in carbonates than in their respective silica…

[Phys. Rev. B 94, 104112] Published Fri Sep 23, 2016

]]>We study the effect of electronic Coulomb correlations on the vacancy formation energy in paramagnetic $\alpha \text{\u2212}\mathrm{Fe}$ within *ab initio* dynamical mean-field theory. The calculated value for the formation energy is substantially lower than in standard density-functional calculations and in excellent agreement w…

[Phys. Rev. B 94, 100102(R)] Published Wed Sep 21, 2016

]]>Shock compression of silicon (Si) under extremely high pressures (>100 Mbar) was investigated by using two first-principles methods of orbital-free molecular dynamics (OFMD) and path integral Monte Carlo (PIMC). While pressures from the two methods agree very well, PIMC predicts a second compression …

[Phys. Rev. B 94, 094109] Published Thu Sep 15, 2016

]]>We present an experimental and theoretical study of the optically detected magnetic resonance signals for ensembles of negatively charged nitrogen-vacancy (NV) centers in a ${}^{13}\mathrm{C}$ isotopically enriched single-crystal diamond. We observe four broad transition peaks with superimposed sharp features at ze…

[Phys. Rev. B 94, 094108] Published Wed Sep 14, 2016

]]>Accelerated molecular dynamics reveals a mechanism transition and strong temperature dependence of dislocation nucleation from grain boundaries (GBs) in Cu. At stress levels up to $\sim 90\%$ of the ideal dislocation-nucleation stress, atomic shuffling at the $E$ structural unit in a GB acts as a precursor t…

[Phys. Rev. B 94, 104110] Published Wed Sep 14, 2016

]]>High-temperature atomic configurations of fcc Fe-Cr-Ni alloys with alloy composition close to austenitic steel are studied in statistical thermodynamic simulations with effective interactions obtained in *ab initio* calculations. The latter are done taking longitudinal spin fluctuations (LSF) into con…

[Phys. Rev. B 94, 104111] Published Wed Sep 14, 2016

]]>Using an experimental setup designed to scan a submicron sized light spot and collect the photogenerated current through larger electrodes, we map the photovoltaic response in ferroelectric $\mathrm{BiFe}{\mathrm{O}}_{3}$ single crystals. We study the effect produced by a unique 180° ferroelectric domain wall (DW) and show …

[Phys. Rev. B 94, 094107] Published Mon Sep 12, 2016

]]>Diffusionless displacive lattice rearrangements, which include martensitic transformations, are in real materials often accompanied by a displacive drag of interstitials. The interplay of both processes leads to a particular atomistic arrangement of the interstitials in the product phase, which is d…

[Phys. Rev. B 94, 104109] Published Mon Sep 12, 2016

]]>Two-dimensional (2D) ${\mathrm{BNSi}}_{2}$ has been recently proposed to be a viable candidate material with a graphenelike structure. We have carried out *ab initio* evolutionary ground state searches and uncovered a number of 2D structures in the $\left(\mathrm{BN}\right){}_{x}{\mathrm{Si}}_{1-x}$ pseudobinary system with considerably lower energies. Neve…

[Phys. Rev. B 94, 094105] Published Fri Sep 09, 2016

]]>We explore topological transitions in parameter space in order to enable adiabatic passages between regions adiabatically disconnected within a given parameter manifold. To this end, we study the Hamiltonian of two coupled qubits interacting with external magnetic fields, and make use of the analogy…

[Phys. Rev. B 94, 094106] Published Fri Sep 09, 2016

]]>In this work, a systematic investigation of the alloying behavior on the $M$ sublattice of ${M}_{2}\mathrm{AlC}$, where $M$ is Ti, V, Zr, and Hf with elements in the first transition metal row as well as Ca and Sc is carried out via a combination of alloy theoretic approaches and density functional theory for 41 alloy …

[Phys. Rev. B 94, 104106] Published Fri Sep 09, 2016

]]>The role of quantum ion dynamics in the low melting temperatures of Li is investigated from first principles theory. Free energies of solid and liquid phases are obtained at the classical and quantum ion levels. The results are used to determine the Li melting curve in the 40–60 and 110–150 GPa pres…

[Phys. Rev. B 94, 104107] Published Fri Sep 09, 2016

]]>The exceptionally large piezoelectric response of the morphotropic-phase-boundary (MPB) composition of the lead-free piezoelectric system $(1-x\left)\mathrm{Ba}\right(\mathrm{T}{\mathrm{i}}_{0.8}\mathrm{Z}{\mathrm{r}}_{0.2}){\mathrm{O}}_{3}-x\left(\mathrm{B}{\mathrm{a}}_{0.7}\mathrm{C}{\mathrm{a}}_{0.3}\right)\mathrm{Ti}{\mathrm{O}}_{3}$ has attracted great attention in recent years. Here in this paper we report a detailed investigation of the structural pha…

[Phys. Rev. B 94, 104108] Published Fri Sep 09, 2016

]]>We used *ab initio* random structure searching (AIRSS) to investigate polymorphism in ${\mathrm{C}}_{3}{\mathrm{N}}_{4}$ carbon nitride as a function of pressure. Our calculations reveal new framework structures, including a particularly stable chiral polymorph of space group $P{4}_{3}{2}_{1}2$ containing mixed $s{p}^{2}$ and $s{p}^{3}$ bonding, that we ha…

[Phys. Rev. B 94, 094104] Published Thu Sep 08, 2016

]]>Ferroelectrics that allow a coupling between the polarization and another order parameter are of great interest because they could make the electric field control of nonpolar order parameters possible. In recent years, “hybrid improper’” ferroelectrics - materials where the polarization couples to two different structural distortions - have emerged as a possible way to realize this goal. Theoretical predictions of hybrid improper ferroelectricity in layered perovskite materials were followed by its first experimental realization in Ca${}_{3}$Ti${}_{2}$O${}_{7}$ in 2015. However, the precise pathway by which the polarization reverses in this material during ferroelectric switching remains an open question. The authors address this question and lay the groundwork for understanding the unexpectedly complex domain structure of Ca${}_{3}$Ti${}_{2}$O${}_{7}$, consisting of a network of multiple types of domain walls and topological defects.

[Phys. Rev. B 94, 104105] Published Thu Sep 08, 2016

]]>Spintronics holds the promise of novel functionality and higher device performance, but a massive challenge is to find semiconducting materials with good electronic properties that are also ferromagnetic. Dilute magnetic semiconductors (DMS) such as Mn-doped GaAs have great potential but are notoriously difficult to make, only stabilizing in thin films in most cases. Recently, a promising new class of DMS materials based on the chemistry and structure of iron-based superconductors has been discovered, including the compound (Ba,K)(Zn,Mn)${}_{2}$As${}_{2}$. These materials can be synthesized in bulk form, providing an unprecedented opportunity to study the mechanism of ferromagnetism in semiconductors. In this work, the authors present detailed temperature-dependent characterization of the atomic and magnetic structure of (Ba,K)(Zn,Mn)${}_{2}$As${}_{2}$ using x-ray and neutron pair distribution function techniques, establishing the existence of an unexpected structural distortion on a short length scale and surprisingly robust short-range ferromagnetic correlations that persist even at room temperature. These results fill in important gaps in the experimental understanding of DMS materials and provide valuable guidance to their theoretical description.

[Phys. Rev. B 94, 094102] Published Tue Sep 06, 2016

]]>$\mathrm{G}{\mathrm{e}}_{2}\mathrm{S}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{e}}_{5}$ polycrystalline films either in the trigonal stable phase or in the metastable rock-salt structure have been irradiated with 150 keV ${\mathrm{Ar}}^{+}$ ions. The effects of disorder are studied by electrical, optical, and structural measurements and density functional theory (DFT) simulations. In the met…

[Phys. Rev. B 94, 094103] Published Tue Sep 06, 2016

]]>In general, crystallite size reduction is known to suppress the ferroic order (polarization or magnetization) in ferroelectric and magnetic systems. Using free particles of a giant tetragonality $(c/a\u20131=0.18)$ ferroelectric alloy $\mathrm{BiFe}{\mathrm{O}}_{3}\text{\u2212}\mathrm{PbTi}{\mathrm{O}}_{3}$ as the model system, here we show that the intrinsic size …

[Phys. Rev. B 94, 104104] Published Tue Sep 06, 2016

]]>Polar discontinuity at interfaces plays deterministic roles in charge transport, magnetism, and even superconductivity of functional oxides. To date, most polar discontinuity problems have been explored in heterointerfaces between two dissimilar materials. Here, we show that charged domain walls (CD…

[Phys. Rev. B 94, 100101(R)] Published Fri Sep 02, 2016

]]>Two-dimensional (2D) materials have attracted considerable interest due to their remarkable properties and potential applications for nanoelectronics, electrodes, energy storage devices, among others. However, many well-studied 2D materials lack appreciable conductivity and tunable mechanical streng…

[Phys. Rev. B 94, 104103] Published Fri Sep 02, 2016

]]>Investigation of real two-dimensional systems with Dirac-like electronic behavior under the influence of magnetic field is challenging and leads to many interesting physical results. In this paper we study a 2D graphene model with a particular form of magnetic field as a superposition of a homogeneo…

[Phys. Rev. B 94, 094101] Published Thu Sep 01, 2016

]]>The structural and electronic properties of a series of ${\mathrm{SrMnO}}_{3}$ thin films grown on different substrates leading to different biaxial strains are examined by means of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and electron energy-loss spectroscopy (EE…

[Phys. Rev. B 94, 104101] Published Thu Sep 01, 2016

]]>Molybdenum (Mo) is a transition metal with a wide range of technical applications. There has long been strong interest in its high-pressure behavior, and it is often used as standard for high-pressure experiments. Combining powder x-ray diffraction and dynamic ramp compression, structural and equati…

[Phys. Rev. B 94, 104102] Published Thu Sep 01, 2016

]]>The family of layered ${M}_{n+1}A{X}_{n}$ compounds provides a large class of materials with applications ranging from magnets to high-temperature coatings to nuclear cladding. In this work, we employ a density-functional-theory-based discovery approach to identify a large number of thermodynamically stable ${M}_{n+\mathrm{\dots}}$

[Phys. Rev. B 94, 054116] Published Wed Aug 31, 2016

]]>Synchrotron x-ray diffraction experiments were performed on the network compounds ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_{x}{\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ at temperatures between 15 and 800 K. The ferroelectric phase of the parent ${\mathrm{BaAl}}_{2}{\mathrm{O}}_{4}$ is largely suppressed by substituting a small amount of Sr for Ba and disappears for $x\ge 0.1$. Structural refinements revea…

[Phys. Rev. B 94, 054117] Published Wed Aug 31, 2016

]]>The monoclinic (M) phases in high-performance relaxor-based ferroelectric single crystals have been recognized to be a vital structural factor for the outstanding piezoelectric property. However, due to the complexity of the structure in M phases, the understanding about it is still limited. In this…

[Phys. Rev. B 94, 054115] Published Mon Aug 29, 2016

]]>The quantum anomalous Hall effect (QAHE) originates from a combination of the spin-orbital coupling and the breaking of time-reversal symmetry due to intrinsic ferromagnetic ordering and was recently observed in Cr and V doped magnetic topological insulators (TIs). However, it was only observed at e…

[Phys. Rev. B 94, 054113] Published Fri Aug 26, 2016

]]>A recent quasielastic neutron scattering (QENS) study of hydrogen in heavily deformed fcc palladium provided the first direct measurement of hydrogen pipe diffusion, which has a significantly higher diffusivity and lower activation barrier than in bulk. While *ab initio* estimates of hydrogen diffusio…

[Phys. Rev. B 94, 054114] Published Fri Aug 26, 2016

]]>Crystal of ${\mathrm{GaV}}_{4}{\mathrm{S}}_{8}$, a multiferroic system hosting a Néel-type skyrmion lattice phase, has been investigated by polarized Raman and IR spectroscopy above and below the ferroelectric phase transition. Counts of the observed IR and Raman-active modes belonging to distinct irreducible representations agr…

[Phys. Rev. B 94, 060104(R)] Published Fri Aug 26, 2016

]]>First-principles simulations of the porous layered calcogenide materials ${\mathrm{Li}}_{2}{\mathrm{SnO}}_{3}$ and ${\mathrm{Li}}_{2}{\mathrm{SnS}}_{3}$ are used to study their structures, Li ion mobilities, and their interactions with excess Li. The pristine materials are characterized by a regular pattern of voids within the calcogenide layers which are oc…

[Phys. Rev. B 94, 064108] Published Fri Aug 26, 2016

]]>We introduce the concept of a *reflection quasilattice*, the quasiperiodic generalization of a Bravais lattice with irreducible reflection symmetry. Among their applications, reflection quasilattices are the reciprocal (i.e., Bragg diffraction) lattices for quasicrystals and quasicrystal tilings, such…

[Phys. Rev. B 94, 064107] Published Thu Aug 25, 2016

]]>The evolution of local ferroelectric lattice distortions in multiferroic ${\mathrm{Ge}}_{1-x}{\mathrm{Mn}}_{x}\mathrm{Te}$ is studied by x-ray diffraction, x-ray absorption spectroscopy, and density functional theory. We show that the anion/cation displacements smoothly decrease with increasing Mn content, thereby reducing the ferroelect…

[Phys. Rev. B 94, 054112] Published Fri Aug 19, 2016

]]>The confinement effect of intercalated atoms in van der Waals heterostructures can lead to interesting interactions between the confined atoms or molecules and the overlaying two-dimensional (2D) materials. Here we report the formation of ordered Cu(100) $p(2\times 2)$ oxygen superstructures by oxygen inter…

[Phys. Rev. B 94, 064106] Published Thu Aug 18, 2016

]]>Computationally-guided material discovery is being increasingly employed using a descriptor-based screening through the calculation of a few properties of interest. A precise understanding of the uncertainty associated with first-principles density functional theory calculated property values is imp…

[Phys. Rev. B 94, 064105] Published Tue Aug 16, 2016

]]>We study a system of particles in two dimensions interacting via a dipolar long-range potential $D/{r}^{3}$ and subject to a square-lattice substrate potential $V\left(\mathbf{r}\right)$ with amplitude $V$ and lattice constant $b$. The isotropic interaction favors a hexagonal arrangement of the particles with lattice constant $a$, wh…

[Phys. Rev. B 94, 054110] Published Mon Aug 15, 2016

]]>We present a theoretical scheme to calculate the elastic constants of magnetic materials in the high-temperature paramagnetic state. Our approach is based on a combination of disordered local moments picture and *ab initio* molecular dynamics (DLM-MD). Moreover, we investigate a possibility to enhance…

[Phys. Rev. B 94, 054111] Published Mon Aug 15, 2016

]]>We report on the six-dimensional (6D) structural refinement of three members of the i-$R$-Cd quasicrystals ($R$ = Gd, Dy, Tm) via synchrotron x-ray diffraction from single-grain samples, and show that this series is isostructural to the i-${\mathrm{YbCd}}_{5.7}$ quasicrystal. However, our refinements suggest that the $R$…

[Phys. Rev. B 94, 060103(R)] Published Mon Aug 15, 2016

]]>The light-elemental solutes B, C, N, and O can penetrate the surface of Mg alloys and diffuse during heat treatment or high temperature application, forming undesirable compounds. We investigate the diffusion of these solutes by determining their stable interstitial sites and the interpenetrating ne…

[Phys. Rev. B 94, 054106] Published Fri Aug 12, 2016

]]>An atomic interaction is identified in all perovskite compounds, such as $AB{\mathrm{O}}_{3}$ oxides, that can potentially result in unconventional structures. The term is harmonic in nature and couples the motions of the $A$ cations with the rotations of the oxygen octahedra in the perovskite lattice. When strong en…

[Phys. Rev. B 94, 054107] Published Fri Aug 12, 2016

]]>The tetragonal form of ${\mathrm{ZrO}}_{2}$ is used in a wide range of technologies. In this study, we systematically explore the effect of strain on the relative stability of symmetrically equivalent tetragonal variants of ${\mathrm{ZrO}}_{2}$ using first-principles density functional theory. We focus, in particular, on the role …

[Phys. Rev. B 94, 054108] Published Fri Aug 12, 2016

]]>Dynamic dielectric and piezoelectric constants of ferroelectrics increase proportionally to the amplitude of alternating electric field as a result of hysteretic Rayleigh-type motion of domain walls. Here a hysteresis-free quadratic field dependence of the dynamic dielectric response is experimental…

[Phys. Rev. B 94, 054109] Published Fri Aug 12, 2016

]]>We investigate the thermodynamic stability of carbon-rich icosahedral boron carbide at different compositions, ranging from ${\mathrm{B}}_{4}\mathrm{C}$ to ${\mathrm{B}}_{2}\mathrm{C}$, using first-principles calculations. Apart from ${\mathrm{B}}_{4}\mathrm{C}$, generally addressed in the literature, ${\mathrm{B}}_{2.5}\mathrm{C}$, represented by ${\mathrm{B}}_{10}{\mathrm{C}}_{2}^{p}$(C-C), where ${\mathrm{C}}^{p}$ and (C-C) denote a carbon at…

[Phys. Rev. B 94, 054104] Published Wed Aug 10, 2016

]]>We develop a phase-field model that describes the elastic distortion of a ferroelastic material with cubic anisotropy due to an arbitrary dislocation network and a uniform external load. The dislocation network is characterized using the Nye tensor and enters the formulation via a set of incompatibi…

[Phys. Rev. B 94, 054105] Published Wed Aug 10, 2016

]]>In this paper, we develop a multiscale approach to model intrinsic dissipation under high frequency of vibrations in solids. For vibrations with a timescale comparable to the phonon relaxation time, the local phonon distribution deviates from the equilibrium distribution. We extend the quasiharmonic…

[Phys. Rev. B 94, 064103] Published Wed Aug 10, 2016

]]>The pressure-temperature $\left(P\text{\u2212}T\right)$ phase diagram of ${\mathrm{N}}_{2}\text{\u2212}{\mathrm{O}}_{2}$ mixture with a composition of ${\mathrm{N}}_{2}$-48 mol % ${\mathrm{O}}_{2}$ has been investigated using x-ray diffraction and the phase stability of a hexagonal phase (space group: $P6$*/mmm*), with the kagome lattice examined under high-pressure and low-temperature conditions. Wh…

[Phys. Rev. B 94, 064104] Published Wed Aug 10, 2016

]]>Point defects in the binary group-IV monochalcogenide monolayers of SnS, SnSe, GeS, and GeSe are investigated using density functional theory calculations. Several stable configurations are found for oxygen defects, however, we give evidence that these materials are less prone to oxidation than phos…

[Phys. Rev. B 94, 054103] Published Tue Aug 09, 2016

]]>We present evidence of near-infrared photoluminescence (PL) signature of nitrogen vacancy centers ${\left({\mathrm{N}}_{\mathrm{C}}{\mathrm{V}}_{\mathrm{Si}}\right)}^{-}$ in silicon carbide (SiC). This center exhibits an $S=1$ ground state spin similar to the ${\mathrm{NV}}^{-}$ center in diamond. We have performed photoluminescence excitation measurements at cryogenic temperatur…

[Phys. Rev. B 94, 060102(R)] Published Fri Aug 05, 2016

]]>In this work, using zero kelvin *ab initio* calculations, we revisit the structure and ferroelectric phase transition in antiphase domain boundaries (APBs) in ${\text{SrTiO}}_{3}$ (STO), which has been previously addressed in terms of a phenomenological approach. We confirmed the main qualitative conclusion of the …

[Phys. Rev. B 94, 054102] Published Wed Aug 03, 2016

]]>The nitrogen-vacancy (NV) center in diamond has attractive properties for a number of quantum technologies that rely on the spin angular momentum of the electron and the nuclei adjacent to the center. The nucleus with the strongest interaction is the ${}^{13}\mathrm{C}$ nuclear spin of the first shell. Using this d…

[Phys. Rev. B 94, 060101(R)] Published Wed Aug 03, 2016

]]>${A}_{2}\mathrm{S}{\mathrm{n}}_{2}{\mathrm{O}}_{7}$ $(A=\mathrm{Nd},\text{Sm},\text{Gd},\text{Er},\text{Yb},\text{and Y})$ materials with the pyrochlore structure were irradiated with 2.2 GeV Au ions to systematically investigate disordering of this system in response to dense electronic excitation. Structural modifications were characterized, over multiple length scales, by transmission…

[Phys. Rev. B 94, 064102] Published Wed Aug 03, 2016

]]>Crystal plasticity occurs by deformation bursts due to the avalanchelike motion of dislocations. Here we perform extensive numerical simulations of a three-dimensional dislocation dynamics model under quasistatic stress-controlled loading. Our results show that avalanches are power-law distributed a…

[Phys. Rev. B 94, 064101] Published Tue Aug 02, 2016

]]>Structural and thermal properties of $\mathrm{BiFe}{\mathrm{O}}_{3}$ under compressive epitaxial strain are investigated using a shell model fitted to first-principles calculations. We show that a model developed for the bulk describes properly the behavior of the compound as function of the strain, including the appearance…

[Phys. Rev. B 94, 054101] Published Mon Aug 01, 2016

]]>Strain effects on epitaxial thin films of $\mathrm{LaNi}{\mathrm{O}}_{3}$ grown on different single crystalline substrates are studied by Raman scattering and first-principles simulation. New Raman modes, not present in bulk or fully relaxed films, appear under both compressive and tensile strains, indicating symmetry reduc…

[Phys. Rev. B 94, 014118] Published Fri Jul 29, 2016

]]>Scattering of photons by phonons, or Brillouin scattering, enables manipulation and control of light and has led to revolutionary applications, from slow light to saser and cooling of micromechanical resonators. Recently, enhanced light and sound interaction has been demonstrated in waveguides. Howe…

[Phys. Rev. B 94, 024115] Published Thu Jul 28, 2016

]]>By means of positron annihilation lifetime spectroscopy, we have investigated the native defects present in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$, which belongs to the family of topological insulators. We experimentally demonstrate that selenium vacancy defects $\left({\text{V}}_{\text{Se1}}\right)$ are present in ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$ as-grown samples, and that their charge …

[Phys. Rev. B 94, 014117] Published Wed Jul 27, 2016

]]>Exploration of the vast configuration space encountered in a multicomponent alloy is impossible without a suitable engine like the cluster-expansion (CE) method. While a CE ansatz can be formulated for an arbitrary number of components $n$, the combinatorial explosion of configuration space with incre…

[Phys. Rev. B 94, 014116] Published Mon Jul 25, 2016

]]>We study, by means of an atomistic toy model, the interplay of ferroelastic twin patterns and electrical polarization. Our molecular dynamics simulations reproduce polarity in straight twin walls as observed experimentally. We show, by making contact with continuum theory, that the effect is governe…

[Phys. Rev. B 94, 024114] Published Mon Jul 25, 2016

]]>Amorphous (a)-${\mathrm{HfO}}_{2}$ is a prototype high dielectric constant insulator with wide technological applications. Using *ab initio* calculations we show that excess electrons and holes can trap in a-${\mathrm{HfO}}_{2}$ in energetically much deeper polaron states than in the crystalline monoclinic phase. The electrons and h…

[Phys. Rev. B 94, 020103(R)] Published Thu Jul 21, 2016

]]>Based on first-principles phonon and finite temperature molecular dynamics calculations including spin-orbit coupling, we showed that free-standing single-layer phases of bismuth, namely buckled honeycomb and asymmetric washboard structures named as bismuthene, are stable at high temperature. We stu…

[Phys. Rev. B 94, 014115] Published Wed Jul 20, 2016

]]>Core-shell coating structures and concentration gradient materials may enhance Li-ion battery performance by integrating advantages of core and shell components without introducing unfavorable problems associated with general coatings. The fundamental thermodynamic properties of concentration gradie…

[Phys. Rev. B 94, 014114] Published Tue Jul 19, 2016

]]>Lattice defects are inevitably present in two-dimensional materials, with direct implications on their physical and chemical properties. We show that the formation energy of a lattice defect in buckled two-dimensional crystals is not uniquely defined as it takes different values for different bounda…

[Phys. Rev. B 94, 020102(R)] Published Tue Jul 19, 2016

]]>The wavelength dependence of the threshold for femtosecond optical breakdown in water provides information on the interplay of multiphoton, tunneling, and avalanche ionization and is of interest for parameter selection in laser surgery. We measured the bubble threshold from ultraviolet to near-infra…

[Phys. Rev. B 94, 024113] Published Mon Jul 18, 2016

]]>The structural evolution with pressure in bulk $\mathrm{Mo}{\mathrm{S}}_{2}$ has been investigated by high-pressure x-ray diffraction using synchrotron radiation. We found that the out-of-plane S-Mo-S bond angle θ increases and that in in-plane angle $\varphi $ decreases linearly with increasing pressure across the known semiconduct…

[Phys. Rev. B 94, 020101(R)] Published Fri Jul 15, 2016

]]>We report synchrotron x-ray diffraction investigations of interfacially engineered oxygen octahedral rotations and their impact on strain relief in perovskite $\mathrm{SrRu}{\mathrm{O}}_{3}$ films. We show that octahedral rotations with distinct patterns and magnitudes can be accommodated into coherently grown films. The $\mathrm{Sr\dots}$

[Phys. Rev. B 94, 024112] Published Fri Jul 15, 2016

]]>Icosahedral quasicrystals (IQCs) with extremely high degrees of translational order have been produced in the laboratory and found in naturally occurring minerals, yet questions remain about how IQCs form. In particular, the fundamental question of how locally determined additions to a growing clust…

[Phys. Rev. B 94, 014113] Published Thu Jul 14, 2016

]]>We discuss a fundamental theory of how to calculate the phonon-loss sector of the energy-loss spectrum for electrons scattering from crystalline solids. A correlated model for the atomic motion is used for calculating the vibrational modes. Spectra are calculated for crystalline silicon illuminated …

[Phys. Rev. B 94, 014110] Published Wed Jul 13, 2016

]]>Many earlier high-resolution x-ray studies of criticality seemingly invalidated the single-length scaling hypothesis that is predicted by the three-dimensional Ising model, a cornerstone in the theory of critical phenomena. Speculations about the reasons for these discrepancies have concentrated on the role of impurities and on surface-induced strain in the crystalline samples. The general validity of the Ising model for real systems has also been questioned. Here, the authors present x-ray scattering data on the temperature-induced order-disorder transition in $\beta $-brass, nature’s archetypical realization of the Ising model. These investigations unambiguously show that the Ising model does precisely describe the critical behavior observed and, in particular, that the short-range order parameter indeed exhibits single-length scaling. The surface sensitivity has been varied in the experiments without any substantial differences observed.

[Phys. Rev. B 94, 014111] Published Wed Jul 13, 2016

]]>The pressure evolution of the local structure of ${\mathrm{Fe}}_{2}{\mathrm{O}}_{3}$ hematite has been determined by extended x-ray absorption fine structure up to $\sim 79$ GPa. Below the phase-transition pressure at $\sim 50$ GPa, no increasing of ${\mathrm{FeO}}_{6}$ octahedra distortion is observed as pressure is applied. Above the phase transition, an…

[Phys. Rev. B 94, 014112] Published Wed Jul 13, 2016

]]>Interatomic interactions and ordering in fcc Ni-rich Ni-Re alloys are studied by means of first-principles methods combined with statistical mechanics simulations based on the Ising Hamiltonian. First-principles calculations are employed to obtain effective chemical and strain-induced interactions, …

[Phys. Rev. B 94, 024111] Published Wed Jul 13, 2016

]]>We perform density functional calculations to investigate the structure of the intermetallic alloy FeRh under epitaxial strain. Bulk FeRh exhibits a metamagnetic transition from a low-temperature antiferromagnetic (AFM) phase to a ferromagnetic phase at 350 K, and its strain dependence is of interes…

[Phys. Rev. B 94, 014109] Published Tue Jul 12, 2016

]]>In 1949, Forsbergh, Jr. reported spontaneous spatial ordering in the birefringence patterns seen in flux-grown $\mathrm{BaTi}{\mathrm{O}}_{3}$ crystals under the transmission polarized light microscope [Phys. Rev. **76**, 1187 (1949)]. Stunningly regular square-net arrays were often only found within a finite temperature window…

[Phys. Rev. B 94, 024109] Published Tue Jul 12, 2016

]]>The phenomenon of self-organization of domains into a “square-net pattern” in single-crystal, flux-grown $\mathrm{BaTi}{\mathrm{O}}_{3}$ several degrees below the ferroelectric to paraelectric phase transition was investigated using *in situ* synchrotron x-ray topography. The tetragonal distortion of the crystal was determine…

[Phys. Rev. B 94, 024110] Published Tue Jul 12, 2016

]]>We present a scanning tunneling microscopy (STM) study of the domain evolution across two first-order phase transitions of stripe modulations in ${\mathrm{IrTe}}_{2}$ that occur at ${T}_{\mathrm{C}}\approx 275$ K and ${T}_{\mathrm{S}}\approx 180$ K, respectively. Phase coexistence of the hexagonal $(1\times 1)$ structure and the $(5\times 1)$ stripe modulation is observed at ${\dots}_{}$

[Phys. Rev. B 94, 014106] Published Mon Jul 11, 2016

]]>At variance with structural ferroic phase transitions which give rise to macroscopic tensors coupled to macroscopic fields, criteria defining antiferroelectric (AFE) phase transitions are still under discussion due to the absence of specific symmetry properties characterizing their existence. They a…

[Phys. Rev. B 94, 014107] Published Mon Jul 11, 2016

]]>Current materials-related calculations employ density-functional theory (DFT), commonly using the (semi-)local-density approximations for the exchange-correlation (xc) functional. The difficulties in arriving at a reasonable description of van der Waals (vdW) interactions by DFT-based models is to d…

[Phys. Rev. B 94, 024108] Published Mon Jul 11, 2016

]]>We study the temperature-dependent evolution of the octahedral tilt order in a lead-free relaxor ferroelectric and its impact on the ferroelectric properties. Using diffuse neutron scattering on a $0.964{\mathrm{Na}}_{1/2}{\mathrm{Bi}}_{1/2}{\mathrm{TiO}}_{3}\text{\u2212}0.036{\mathrm{BaTiO}}_{3}$ single crystal, we suggest a model for the temperature-dependent nanost…

[Phys. Rev. B 94, 014105] Published Fri Jul 08, 2016

]]>Although defect clusters are detrimental to the electronic and mechanical properties of semiconductor materials, annihilation of such clusters is limited by their lack of thermal mobility due to high migration barriers. Here, we find that small clusters in bulk SiC (a covalent material of importance…

[Phys. Rev. B 94, 024107] Published Fri Jul 08, 2016

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