We study the structural evolution of ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ as a function of pressure using x-ray diffraction. At a pressure of 54 GPa at room temperature, we observe a first-order structural phase transition, associated with a change from tetragonal to monoclinic symmetry and accompanied by a 4% volume collapse.…

[Phys. Rev. B 93, 174118] Published Tue May 31, 2016

]]>$\mathrm{LaOBi}{\mathrm{S}}_{2}$-type materials have drawn much attention recently because of various interesting physical properties, such as low-temperature superconductivity, hidden spin polarization, and electrically tunable Dirac cones. However, it was generally assumed that each $\mathrm{LaOBi}{\mathrm{S}}_{2}$-type compound has a unique and …

[Phys. Rev. B 93, 174119] Published Tue May 31, 2016

]]>Ferroelectrics form domain patterns that minimize their energy subject to imposed boundary conditions. In a linear, constrained theory, that neglects domain-wall energy, periodic domain patterns in the form of multirank laminates can be identified as minimum-energy states. However, when these lamina…

[Phys. Rev. B 93, 174120] Published Tue May 31, 2016

]]>We present a structural analysis of the substituted system $({\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_{x}){\mathrm{CuSi}}_{2}{\mathrm{O}}_{6}$, which reveals a stable tetragonal crystal structure down to 1.5 K. We explore the structural details with low-temperature neutron and synchrotron powder diffraction, room-temperature, and cryogenic high-resolution NMR, as …

[Phys. Rev. B 93, 174121] Published Tue May 31, 2016

]]>Samarium orthoferrite $\left(\mathrm{SmFe}{\mathrm{O}}_{3}\right)$ has been the subject of debate on the existence or nonexistence of ferroelectric properties. It has a high spin-reorientation transition temperature ${T}_{\mathrm{SR}}$ (480 K). Detailed synchrotron x-ray diffraction and Raman spectroscopy dielectric investigations in the 300 to 600 K…

[Phys. Rev. B 93, 174117] Published Thu May 26, 2016

]]>We probe here the optical relaxation properties of Mg-doped wide-band-gap ${\mathrm{LiNbO}}_{3}$ single crystals with both a high spectral and temporal resolution at cryogenic temperatures. Surprisingly, we observe the photoluminescence to decay in a two-step process: a fast relaxation and a slower one centered aro…

[Phys. Rev. B 93, 174116] Published Wed May 25, 2016

]]>We report the structural changes of three $\mathrm{YF}{\mathrm{e}}_{2}{\mathrm{O}}_{4-\delta}$ ($\delta <0.1$) specimens using high resolution synchrotron x-ray powder diffraction between 80 and 300 K. All samples adopt a rhombohedral cell at room temperature (space group $R\overline{3}m$). This cell becomes unstable for the three samples on cooling, and the …

[Phys. Rev. B 93, 184110] Published Wed May 25, 2016

]]>Electric fields are known to favor long-range polar order through the aligning of electric dipoles in relation to Coulomb's force. Therefore, it would be surprising to observe a disordered polar state induced from an ordered state by electric fields. Here we show such an unusual phenomenon in a poly…

[Phys. Rev. B 93, 174114] Published Tue May 24, 2016

]]>Local distortions of the ideal periodic structure in crystals around impurity atoms play an important role in various physical properties of materials. The aim of this study was to investigate the static distortions around cadmium impurity atoms in a ${\text{SnCd}}_{0.0026}$ single crystal using atomic resolution…

[Phys. Rev. B 93, 174115] Published Tue May 24, 2016

]]>A metallic state enabled by the metal-insulator transition (MIT) in single crystal $\mathrm{V}{\mathrm{O}}_{2}\left(\mathrm{A}\right)$ nanorods is demonstrated, which provides important physical foundation in experimental understanding of MIT in $\mathrm{V}{\mathrm{O}}_{2}$. The observed tetragonal metallic state at ∼28 GPa should be interpreted as a distinct metastab…

[Phys. Rev. B 93, 184109] Published Tue May 24, 2016

]]>Accurate theoretical calculations of the nonlinear elastic response of strong solids (e.g., diamond) constitute a fundamental and important scientific need for understanding the response of such materials and for exploring the potential synthesis and design of novel solids. However, without correspo…

[Phys. Rev. B 93, 174113] Published Mon May 23, 2016

]]>Variation of the phase of the beam transmitted through a crystalline material as a function of the rocking angle is a well-known dynamical effect in x-ray scattering. Unfortunately, it is not so easy to directly measure these phase variations in a conventional scattering experiment. It was recently …

[Phys. Rev. B 93, 184107] Published Mon May 23, 2016

]]>A correct description of hydrogen diffusion and trapping is the prerequisite for an understanding of the phenomenon of hydrogen embrittlement. In this study, we carried out extensive first-principles calculations based on density functional theory to investigate the interaction of H with TiC precipi…

[Phys. Rev. B 93, 184108] Published Mon May 23, 2016

]]>The metal-insulator switching characteristics of ${\mathrm{VO}}_{2}$ play a crucial role in the performances of ${\mathrm{VO}}_{2}$-based devices. In this paper we study high-quality (010)-oriented epitaxial films grown on (001) sapphire substrates by means of electron-beam evaporation and investigate the role of interface defects…

[Phys. Rev. B 93, 184106] Published Fri May 20, 2016

]]>The traditional derivation of the elastic anomalies associated with ferroelectric (FE) phase transitions in the framework of the Landau theory is combined with the piezoelectric constitutive relations instead of being explicitly carried out with a definite expression of the FE part of the free energ…

[Phys. Rev. B 93, 174111] Published Thu May 19, 2016

]]>The structural and mechanical properties of N-doped graphene (NG) are investigated using reactive force field (ReaxFF) potentials in large-scale molecular dynamics simulations. We found that ripples, which are induced by the dopants, change the roughness of NG, which depends on the number of dopants…

[Phys. Rev. B 93, 174112] Published Thu May 19, 2016

]]>Bragg coherent x-ray diffractive imaging is a powerful technique for investigating dynamic nanoscale processes in nanoparticles immersed in reactive, realistic environments. Its temporal resolution is limited, however, by the oversampling requirements of three-dimensional phase retrieval. Here, we s…

[Phys. Rev. B 93, 184105] Published Thu May 19, 2016

]]>The mechanical properties and electronic structure of polymorphic tungsten carbides with different stacking sequences have been investigated by means of density functional theory. The stacking sequence strongly influences the stability and mechanical strength of these polymorphs. Using the plastic p…

[Phys. Rev. B 93, 184104] Published Wed May 18, 2016

]]>We report a density-functional study on the evolution of the electronic and lattice structure in ${\mathrm{BiFeO}}_{3}$ with injected electrons and holes. First, the self-trapping of electrons and holes was investigated. We found that the injected electrons tend to be localized on Fe sites due to the local lattice …

[Phys. Rev. B 93, 174110] Published Tue May 17, 2016

]]>The atomic and electronic structures of ${60}^{\circ}$ glide perfect and ${30}^{\circ}/{90}^{\circ}$ glide partial dislocations in CdTe are studied using combined semi-empirical and density functional theory calculations. The calculations predict that the dislocation cores tend to undergo significant reconstructions along the dis…

[Phys. Rev. B 93, 174109] Published Mon May 16, 2016

]]>The role of oxygen doping in CdTe is addressed by first-principles calculations. Formation energies, charge transition levels, and quasiparticle defect states are calculated within the $\text{DFT}+GW$ formalism. The formation of a new defect is identified, the $\left({\text{O}}_{\text{Te}}{\text{-Te}}_{\text{Cd}}\right)$ complex. This complex is energeticall…

[Phys. Rev. B 93, 184103] Published Mon May 16, 2016

]]>We extend the nested sampling algorithm to simulate materials under periodic boundary and constant pressure conditions, and show how it can be used to determine the complete equilibrium phase diagram for a given potential energy function, efficiently and in a highly automated fashion. The only input…

[Phys. Rev. B 93, 174108] Published Fri May 13, 2016

]]>Using first-principles calculations based on density functional theory, we have studied the mechanical, electronic, and magnetic properties of Heusler alloys, namely, ${\mathrm{Ni}}_{2}BC$ and ${\mathrm{Co}}_{2}BC$ ($B$ = Sc, Ti, V, Cr, and Mn as well as Y, Zr, Nb, Mo, and Tc; $C$ = Ga and Sn). On the basis of electronic structure (de…

[Phys. Rev. B 93, 184102] Published Fri May 13, 2016

]]>To achieve a fundamental understanding of the multiferroic behavior and electronic properties of intrinsic vacancies in $\mathrm{BiFe}{\mathrm{O}}_{3}$, here we performed first-principles calculations based on hybrid Hartree-Fock density functional theories, which can accurately describe defect electronic structures. Oxygen…

[Phys. Rev. B 93, 174107] Published Thu May 12, 2016

]]>We propose a method to measure the hyperfine vectors between a nitrogen-vacancy (NV) center and an environment of interacting nuclear spins. Our protocol enables the generation of tunable electron-nuclear coupling Hamiltonians while suppressing unwanted internuclear interactions. In this manner, eac…

[Phys. Rev. B 93, 174104] Published Tue May 10, 2016

]]>Hydrogen sulfide $\left({\mathrm{H}}_{2}\mathrm{S}\right)$ was studied by x-ray synchrotron diffraction and Raman spectroscopy up to 150 GPa at 180–295 K and by quantum-mechanical variable-composition evolutionary simulations. The experiments show that ${\mathrm{H}}_{2}\mathrm{S}$ becomes unstable with respect to formation of compounds with different structur…

[Phys. Rev. B 93, 174105] Published Tue May 10, 2016

]]>Premelting or virtual melting was proposed previously as an important deformation mechanism for high strain-rate loading. However, two questions remain outstanding: how premelting occurs exactly, and whether it plays a role in plastic deformation independent of, parasitic on, or synergetic with, dis…

[Phys. Rev. B 93, 174106] Published Tue May 10, 2016

]]>Limit-periodic structures are well ordered but nonperiodic, and hence have nontrivial vibrational modes. We study a ball and spring model with a limit-periodic pattern of spring stiffnesses and identify a set of extended modes with arbitrarily low participation ratios, a situation that appears to be…

[Phys. Rev. B 93, 174102] Published Mon May 09, 2016

]]>Τhe magnetoelectric $\mathrm{ZnC}{\mathrm{r}}_{2}\mathrm{S}{\mathrm{e}}_{4}$ spinel, with space group $Fd\overline{3}m$, undergoes a reversible first-order structural transition initiating at 17 GPa, as revealed by our high-pressure x-ray diffraction studies at room temperature. We tentatively assign the high-pressure modification to an $A\mathrm{M}{\mathrm{o}}_{2}{\mathrm{S}}_{4}$-type phase, a …

[Phys. Rev. B 93, 174103] Published Mon May 09, 2016

]]>The origin of ferroelectric polarization in tetragonal tungsten-bronze- (TTB-) type oxide strontium barium niobate (SBN) is investigated using first-principles density functional calculations. We study in particular the relationship between the polarization and the cation and vacancy ordering on alk…

[Phys. Rev. B 93, 180101(R)] Published Mon May 09, 2016

]]>In a ferroelectric helimagnetic phase of a spin-driven multiferroic, ${\mathrm{CuFeO}}_{2}$, we find irreversibly additive evolution of electric polarization $P$ induced by sweeping magnetic field $H$ under an applied electric field $E$, despite a large coercive electric field in the phase. From the unpolarized neutron d…

[Phys. Rev. B 93, 174101] Published Tue May 03, 2016

]]>We demonstrate that the melting points and other thermodynamic quantities of the alkali metals can be calculated based on static crystalline properties. To do this we derive analytic interatomic potentials for the alkali metals fitted precisely to cohesive and vacancy energies, elastic moduli, the l…

[Phys. Rev. B 93, 184101] Published Mon May 02, 2016

]]>We introduce an algorithm for the reconstruction of the complex transmission function of a specimen using segmented detectors in scanning transmission electron microscopy geometry. The phase of the transmission function can be related to magnetic and electric fields within the specimen and is sensit…

[Phys. Rev. B 93, 134116] Published Wed Apr 27, 2016

]]>Oxygen vacancies in ${\mathrm{LaAlO}}_{3}$ (LAO) play an important role in the formation of the two-dimensional electron gas observed at the ${\mathrm{LaAlO}}_{3}\text{/}{\mathrm{SrTiO}}_{3}$ interface and affect the performance of MOSFETs using LAO as a gate dielectric. However, their spectroscopic properties are still poorly understood, which hamper…

[Phys. Rev. B 93, 134114] Published Mon Apr 25, 2016

]]>A formalism for the vacancy formation energies in random alloys within the single-site mean-filed approximation, where vacancy-vacancy interaction is neglected, is outlined. It is shown that the alloy configurational entropy can substantially reduce the concentration of vacancies at high temperature…

[Phys. Rev. B 93, 134115] Published Mon Apr 25, 2016

]]>Segregation-induced structural transitions in metallic grain boundaries are studied with hybrid atomistic Monte Carlo/molecular dynamics simulations using Cu-Zr as a model system, with a specific emphasis on understanding the effect of grain boundary character. With increasing global composition, th…

[Phys. Rev. B 93, 134113] Published Fri Apr 22, 2016

]]>The effect of external mechanical fields on relaxor $0.94\left(\mathrm{N}{\mathrm{a}}_{1/2}\mathrm{B}{\mathrm{i}}_{1/2}\right)\mathrm{Ti}{\mathrm{O}}_{3}\text{\u2212}0.06\mathrm{BaTi}{\mathrm{O}}_{3}$ was investigated by means of temperature- and stress-dependent dielectric constant measurements between 223 and 673 K. Analogous to previous investigations that showed an electric-field-induced ferroelectric long-ran…

[Phys. Rev. B 93, 134111] Published Wed Apr 20, 2016

]]>We studied the microscopic mechanism of the paraelectric-ferroelectric (PE-FE) phase transition of ${\mathrm{CsH}}_{2}{\mathrm{PO}}_{4}$ (CDP) by means of first-principles electronic structure calculations. The calculated structural parameters in the PE and FE phases as well as the total spontaneous polarization ${P}_{s}$ obtained with…

[Phys. Rev. B 93, 134112] Published Wed Apr 20, 2016

]]>High-resolution single crystal neutron diffraction measurements are presented probing the magnetostructural response to uniaxial pressure in the iron pnictide parent system ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$. Scattering data reveal a strain-activated, anisotropic broadening of nuclear Bragg reflections, which increase upon c…

[Phys. Rev. B 93, 144118] Published Wed Apr 20, 2016

]]>High-pressure solid-state transformations at high strain rates are usually observed after the fact, either during static holding or after unloading, or inferred from interferometry measurements of the sample surface. The emergence of femtosecond x-ray diffraction techniques provides insight into the…

[Phys. Rev. B 93, 144119] Published Wed Apr 20, 2016

]]>A complete structural solution of the bilayer iridate compound ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ presently remains outstanding. Previously reported structures for this compound vary and all fail to explain weak structural violations observed in neutron scattering measurements as well as the presence of a net ferromagnetic m…

[Phys. Rev. B 93, 134110] Published Tue Apr 19, 2016

]]>A new ground state of textbook compound strontium titanate $\left(\mathrm{SrTi}{\mathrm{O}}_{3}\right)$ is obtained by inducing a specific core-shell structure of the particles. Using a combination of high energy synchrotron and neutron diffraction, we demonstrate a lowering of the ferroelastic ground state towards a new antiferrodist…

[Phys. Rev. B 93, 144117] Published Tue Apr 19, 2016

]]>We investigated the structural phase transition of ${\mathrm{BaAl}}_{2}{\mathrm{O}}_{4}$, which has a network structure with corner-sharing ${\mathrm{AlO}}_{4}$ tetrahedra, via synchrotron x-ray thermal diffuse scattering measurements and first-principles calculations. ${\mathrm{BaAl}}_{2}{\mathrm{O}}_{4}$ shows the structural phase transition at ${T}_{\mathrm{C}}=451.4$ K from the $P{6}_{3}22$ p…

[Phys. Rev. B 93, 134108] Published Mon Apr 18, 2016

]]>The local structure of ${\mathrm{IrTe}}_{2}$ has been studied by iridium ${L}_{3}$-edge x-ray absorption spectroscopy (XAS) measurements as a function of pressure, performed at two temperatures (100 and 295 K) across the structural phase transition at $\sim 270$ K. Extended x-ray absorption fine structure (EXAFS) and x-ray abso…

[Phys. Rev. B 93, 134109] Published Mon Apr 18, 2016

]]>By means of circularly polarized x rays at the Dy ${L}_{3}$ and Fe $K$ absorption edges, the chiral structure of the electric quadrupole was investigated for a single crystal of ${\mathrm{DyFe}}_{3}$(${\mathrm{BO}}_{3}$)${}_{4}$, in which both Dy and Fe ions exhibit a spiral arrangement. The integrated intensity of the resonant x-ray diffraction …

[Phys. Rev. B 93, 144116] Published Mon Apr 18, 2016

]]>We discuss the influence of site occupancy on the absorption of the hydrogen isotopes H and D in thin V(001) layers. By growing V(001) under biaxial compressive strain in Fe/V(001) superlattices, the hydrogen (H as well as D) is forced to reside exclusively in octahedral (${\mathrm{O}}_{z}$) sites, even at the lowe…

[Phys. Rev. B 93, 134107] Published Fri Apr 15, 2016

]]>To explore the microscopic response of a metallic glass (MG) to an applied hydrostatic load we performed a high-pressure extended x-ray absorption fine structure (EXAFS) study of the ${\mathrm{Zr}}_{66.7}{\mathrm{Cu}}_{33.3}$ amorphous alloy. EXAFS fitting revealed that on compression, Zr-Zr pairs are strained preferentially. St…

[Phys. Rev. B 93, 144115] Published Fri Apr 15, 2016

]]>$\mathrm{N}{\mathrm{a}}_{0.5}\mathrm{B}{\mathrm{i}}_{0.5}\mathrm{Ti}{\mathrm{O}}_{3}$- based lead-free piezoelectrics exhibiting giant piezostrain are technologically interesting materials for actuator applications. The lack of clarity with regard to the structure of the nonpolar phase of this system has hindered the understanding of the structural mechanism associated…

[Phys. Rev. B 93, 134106] Published Thu Apr 14, 2016

]]>We report the thermodynamic potential for single-domain (110) thin films epitaxially grown on dissimilar cubic substrates. Using different sets of paraelectric phase elastic compliance coefficients of ${\mathrm{PbTiO}}_{3}$ single crystal, calculated from the experimental room-temperature values, we predict rotatio…

[Phys. Rev. B 93, 144113] Published Thu Apr 14, 2016

]]>We study the topological properties of three-dimensional (3D) Floquet band structures, which are defined using unitary evolution matrices rather than Hamiltonians. Previously, two-dimensional band structures of this sort have been shown to exhibit anomalous topological behaviors, such as topological…

[Phys. Rev. B 93, 144114] Published Thu Apr 14, 2016

]]>Graphite is a prototypical solid lubricant demanding a thorough understanding of its low-friction behavior. The ${E}_{2g}$(1) Raman active vibrational mode of graphite is associated with the rigid-layer relative movement of its graphene sheets. Thus, this mode can provide a good means of exploring the low …

[Phys. Rev. B 93, 144112] Published Wed Apr 13, 2016

]]>An absolute stress-density path for shocklessly compressed copper is obtained to over 450 GPa. A magnetic pressure drive is temporally tailored to generate shockless compression waves through over 2.5-mm-thick copper samples. The free-surface velocity data is analyzed for Lagrangian sound velocity u…

[Phys. Rev. B 93, 134105] Published Tue Apr 12, 2016

]]>$\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{39}\mathrm{G}{\mathrm{e}}_{7}$ and $\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{29}\mathrm{G}{\mathrm{e}}_{17}$ have been studied at high pressure using x-ray diffraction and x-ray absorption spectroscopy (XAS) at the Ge $K$ edge. In $\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{39}\mathrm{G}{\mathrm{e}}_{7}$, a transition is observed similar to the one in $\mathrm{B}{\mathrm{a}}_{8}\mathrm{S}{\mathrm{i}}_{46}$, apparently isostructural. However, the XAS data analysis shows that the transformatio…

[Phys. Rev. B 93, 134103] Published Mon Apr 11, 2016

]]>The continuous electron bombardment of a sample during transmission electron microscopy (TEM) drives atomic-scale transformations. In earlier studies the transformations appeared to proceed as if the sample was held at an elevated temperature, and, indeed, the hypothesis of an electron-beam-induced …

[Phys. Rev. B 93, 134104] Published Mon Apr 11, 2016

]]>Simultaneous thermal, acoustic, and magnetic emission (AE and ME) measurements during thermally induced martensitic transformation in ${\text{Ni}}_{2}\text{MnGa}$ single crystals demonstrate that all three types of the above noises display many coincident peaks and the same start and finish temperatures. The amplitude a…

[Phys. Rev. B 93, 144108] Published Mon Apr 11, 2016

]]>The authors have used resonant ultrasound spectroscopy to characterize variations in the elastic and anelastic properties of GeTe associated with the ferroelectric/ferroelastic phase transition at ~625 K. These arise as a consequence of strong coupling between strain and driving order parameter, and their magnitudes are permissive of a significant order/disorder component to the transition. Remarkably, precursor softening due to dynamical disorder and Debye freezing of twin walls at low temperatures appear both to be controlled by the same thermally activated mechanism associated with small displacements of Ge within GeTe${}_{6}$ octahedra. This mechanism must also be important in constraining the stability and dynamics with respect to ferroelectric switching.

[Phys. Rev. B 93, 144109] Published Mon Apr 11, 2016

]]>An interatomic potential model that can simultaneously describe metallic, covalent, and ionic bonding is suggested by combining the second nearest-neighbor modified embedded-atom method (2NNMEAM) and the charge equilibration (Qeq) method, as a further improvement of a series of existing models. Payi…

[Phys. Rev. B 93, 144110] Published Mon Apr 11, 2016

]]>One of the key impediments to the development of ${\mathrm{BaTiO}}_{3}$-based materials as candidates to replace toxic-Pb-based solid solutions is their relatively low ferroelectric Curie temperature (${T}_{C}$). Among many potential routes that are available to modify ${T}_{C}$, ionic substitutions at the Ba and Ti sites remain…

[Phys. Rev. B 93, 144111] Published Mon Apr 11, 2016

]]>Noting the structural relationships between phases of carbon and boron carbide with phases of boron nitride and boron subnitride, we investigate their mutual solubilities using a combination of first-principles total energies supplemented with statistical mechanics to address finite temperatures. Th…

[Phys. Rev. B 93, 144107] Published Fri Apr 08, 2016

]]>Organic and inorganic lead halogen perovskites, and in particular, $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Pb}{\mathrm{I}}_{3}$, have during the last years emerged as a class of highly efficient solar cell materials. Herein we introduce metalorganic halogen perovskite materials for energy-relevant applications based on alkaline-earth metals. Based …

[Phys. Rev. B 93, 144105] Published Thu Apr 07, 2016

]]>We perform density functional theory based first-principles calculations to identify promising alloying elements $\left(X\right)$ capable of enhancing the compressive uniaxial theoretical (ideal) strength of the fcc Ni-matrix along the $\u2329001\u232a$ direction. The alloying element belongs to a wide range of $3d,4d$, and $5d$ …

[Phys. Rev. B 93, 144106] Published Thu Apr 07, 2016

]]>${\mathrm{Ni}}_{2}\mathrm{MnGa}$ exhibits ideal ferromagnetic shape memory properties, however, brittleness and a low-temperature martensite transition hinder its technological applications motivating the search for novel materials showing better mechanical properties as well as higher transition temperatures. In this work,…

[Phys. Rev. B 93, 134102] Published Wed Apr 06, 2016

]]>The ${\mathrm{Li}}_{13}{\mathrm{Si}}_{4}$ phase is one out of several crystalline lithium silicide phases, which is a potential electrode material for lithium ion batteries and contains a high theoretical specific capacity. By means of *ab initio* methods like density functional theory (DFT) many properties such as heat capacity o…

[Phys. Rev. B 93, 144104] Published Wed Apr 06, 2016

]]>We report modifications of the ferroelectric and electrocaloric properties of ${\mathrm{BaTiO}}_{3}$ by defects. For this purpose, we have combined *ab initio* based molecular dynamics simulations with a simple model for defects. We find that different kinds of defects modify the ferroelectric transition temperatures…

[Phys. Rev. B 93, 134101] Published Tue Apr 05, 2016

]]>The electronic structure and magnetic properties of a single Fe adatom on a CuN surface have been studied using density functional theory in the local spin density approximation (LSDA), the LSDA+U approach, and the local density approximation plus dynamical mean-field theory (LDA+DMFT). The impurity…

[Phys. Rev. B 93, 140101(R)] Published Mon Apr 04, 2016

]]>Using a combination of first-principles calculation and high-resolution scanning TEM, the authors report novel structural characteristics of the ferreoelastic 90${}^{\circ}$ domain wall in PbTiO${}_{3}$. They highlight the discovery of a sharp discontinuity in the variation of the lattice parameters across the domain wall. The first-principles calculations show that oxygen vacancies prefer to cluster in the plane adjacent to the asymmetric domain walls. Understanding interaction of oxygen vacancies with domain walls is important because such defects are used to tailor properties of ferroelectric materials

[Phys. Rev. B 93, 144102] Published Mon Apr 04, 2016

]]>Semiconductors under femtosecond x-ray irradiation are transiently excited to nonequilibrium states. This can lead to observable material modifications. During the excitation and relaxation dynamics, optical properties of the solid are changing, affected by both transient electron excitation as well…

[Phys. Rev. B 93, 144101] Published Fri Apr 01, 2016

]]>We use *ab initio* calculations to estimate the formation energies of cation (transition-metal) antisite defects at oxide interfaces and to understand the basic physical effects that drive or suppress the formation of these defects. Antisite defects are found to be favored in systems with substantial …

[Phys. Rev. B 93, 104111] Published Thu Mar 31, 2016

]]>We present a scaling law for the energy and speed of transition waves in dissipative and diffusive media. By considering uniform discrete lattices and continuous solids, we show that—for arbitrary highly nonlinear many-body interactions and multistable on-site potentials—the kinetic energy per densi…

[Phys. Rev. B 93, 104109] Published Wed Mar 30, 2016

]]>We study the lowest energy configurations of an equimolar binary mixture of classical pointlike particles with charges ${Q}_{1}$ and ${Q}_{2}$, such that $q={Q}_{2}/{Q}_{1}\in [0,1]$. The particles interact pairwise via three-dimensional (3D) Coulomb potential and are confined to a 2D plane with a homogeneous neutralizing backg…

[Phys. Rev. B 93, 104110] Published Wed Mar 30, 2016

]]>Several Tl and Pb based halides and chalcohalides have recently been discovered as promising optoelectronic materials [i.e., photovoltaic (PV) and gamma-ray detection materials]. Efficient carrier transport in these materials is attributed partly to the special chemistry of $n{s}^{2}$ ions (e.g., $\mathrm{T}{\mathrm{l}}^{+},\mathrm{P}{\mathrm{b}}^{2+}$…

[Phys. Rev. B 93, 104108] Published Tue Mar 29, 2016

]]>We performed diffusion Monte Carlo (DMC) calculations of the spectroscopic properties of a large set of molecules, assessing the effect of different approximations. In systems containing elements with large atomic numbers, we show that the errors associated with the use of nonlocal mean-field-based …

[Phys. Rev. B 93, 094111] Published Mon Mar 28, 2016

]]>Mixed magnetism (the coexistence of strong and weak magnetism in one material) is regarded as the origin of the giant magnetocaloric effect (GMCE). A good example is ${(\mathrm{Mn},\mathrm{Fe})}_{2}(\mathrm{Si},\mathrm{P})$, which is established as one of the best magnetocaloric materials available. Tuning the material properties are essenti…

[Phys. Rev. B 93, 094110] Published Fri Mar 25, 2016

]]>First-principles calculations are presented to resolve the possible pressure-dependent phases of ${\mathrm{Mg}}_{2}\mathrm{Si}$. Although previous reports show that ${\mathrm{Mg}}_{2}\mathrm{Si}$ is characterized by the cubic antifluorite $Fm\overline{3}m$ structure at low pressures, the situation at higher pressures is less clear with many contradicting resul…

[Phys. Rev. B 93, 094109] Published Tue Mar 22, 2016

]]>Properties of the $\omega $ structure are investigated for 27 transition elements from the viewpoints of thermodynamical and dynamical stability based on first-principles calculations. The thermodynamical stability of the $\omega $ structure is compared with those of the body-centered-cubic, face-centered-cubic, an…

[Phys. Rev. B 93, 094108] Published Fri Mar 18, 2016

]]>We describe how *ab initio* molecular dynamics can be used to determine the Hugoniot locus (states accessible by a shock wave) for materials with a number of stable phases, and with an approximate treatment of plasticity and yield, without having to simulate these phenomena directly. We consider the c…

[Phys. Rev. B 93, 094107] Published Thu Mar 17, 2016

]]>Some anisotropy in both mechanical and thermodynamical properties of bismuth is expected. A combination of density functional theory total energy calculations and density functional perturbation theory in the local density approximation is used to compute the elastic constants at 0 K using a finite …

[Phys. Rev. B 93, 094106] Published Wed Mar 16, 2016

]]>We have studied the pressure-induced structural and electronic transitions of GeS to 49 GPa, using diamond anvil cells, microconfocal Raman spectroscopy, synchrotron angle-resolved x-ray diffraction, and electrical resistance measurements. The results indicate that layered GeS phase I (*Pnma*) undergo…

[Phys. Rev. B 93, 104107] Published Tue Mar 15, 2016

]]>At ambient pressure the element cerium shows a metastable (${t}_{1/2}\sim 40$ years) double-hexagonal close-packed $\beta $ phase that is positioned between two cubic phases, $\gamma $ and $\alpha $. With modest pressure the $\beta $ phase can be suppressed, and a volume contraction (17%) occurs between the $\gamma $ and the $\alpha $ phases as the temper…

[Phys. Rev. B 93, 094103] Published Mon Mar 14, 2016

]]>The phase-transition sequence of $0.67\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3})-0.37\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-0.37PT) single crystals driven by the electric ($E$) field and temperature is comprehensively studied. Based on the strain-$E$ field loop, polarization-$E$ field loop, and the evolution of domain configurations, the $E$ field along the ${[011\dots}_{}$

[Phys. Rev. B 93, 094104] Published Mon Mar 14, 2016

]]>Organic-inorganic hybrid halide perovskites, in which the A cations of an ${\mathrm{ABX}}_{3}$ perovskite are replaced by organic cations, may be used for photovoltaic and solar thermoelectric applications. In this contribution, we systematically study three lead-free hybrid perovskites, i.e., methylammonium tin io…

[Phys. Rev. B 93, 094105] Published Mon Mar 14, 2016

]]>Local structures in cubic perovskite-type $\left(\mathrm{B}{\mathrm{a}}_{0.6}\mathrm{B}{\mathrm{i}}_{0.4}\right)\left(\mathrm{T}{\mathrm{i}}_{0.6}\mathrm{S}{\mathrm{c}}_{0.4}\right){\mathrm{O}}_{3}$ solid solutions that exhibit reentrant dipole glass behavior have been studied with variable-temperature x-ray/neutron total scattering, extended x-ray absorption fine structure, and electron diffraction methods. Simultaneous fitti…

[Phys. Rev. B 93, 104106] Published Mon Mar 14, 2016

]]>A multifaceted approach is used to identify the Fe centers associated with $\mathrm{KNb}{\mathrm{O}}_{3}:\mathrm{Fe}$, determine the location of energy levels, and conclude which centers play a vital role in the photorefractive effect; with such an understanding, the physical parameters may be modified to provide mature materials fo…

[Phys. Rev. B 93, 094102] Published Thu Mar 10, 2016

]]>The process of deformation twinning, as schematically indicated in the figure, plays an important role in establishing the ductility of many engineering materials such as titanium and magnesium and some refractory alloys. By fine tuning alloy compositions, the tendency for twin formation can be controlled, which can lead to guidelines for design of advanced alloys for applications spanning biomedical, energy conversion, and high-temperature structural applications. This work presents a theoretical framework to computationally study the effect of alloying on planar defect energies and is expected to be a useful tool for computationally guided alloy design.

[Phys. Rev. B 93, 094101] Published Wed Mar 09, 2016

]]>The lattice thermal conductivity (${\kappa}_{\mathrm{L}}$) of ${\mathrm{PbTiO}}_{3}$ is estimated using a combination of *ab initio* calculations and the semiclassical Boltzmann transport equation. The computed ${\kappa}_{\mathrm{L}}$ is remarkably low, nearly comparable with the ${\kappa}_{\mathrm{L}}$ of good thermoelectric materials such as PbTe. In addition, a semiclassical …

[Phys. Rev. B 93, 100101(R)] Published Wed Mar 09, 2016

]]>The redistribution of the electron density in a material during laser irradiation can have a significant impact on its structural dynamics. This electronic excitation can be incorporated into two temperature molecular dynamics (2T-MD) simulations through the use of electronic temperature dependent p…

[Phys. Rev. B 93, 104105] Published Wed Mar 09, 2016

]]>We investigated phonon-phonon interactions in photoexcited single-crystalline graphite by ultrafast electron diffraction. Transient electron diffraction profiles from a 35 nm graphite film were observed following laser excitation. Changes in intensities of diffraction spots revealed a two-exponentia…

[Phys. Rev. B 93, 104104] Published Mon Mar 07, 2016

]]>Quantum Monte Carlo simulations at zero temperature of a ${}^{3}\mathrm{He}$ monolayer adsorbed on graphite, either clean or preplated with ${}^{4}\mathrm{He}$, unexpectedly point to a gas-liquid phase transition at a very low areal density of the order of $0.01\phantom{\rule{4pt}{0ex}}{\AA}^{-2}$. This result stems from an essentially unbiased calculation of the …

[Phys. Rev. B 93, 104102] Published Wed Mar 02, 2016

]]>A comparative study of field-induced domain switching and lattice strain was carried out by *in situ* electric-field-dependent high-energy synchrotron x-ray diffraction on a morphotropic phase boundary (MPB) and a near-MPB rhombohedral/pseudomonoclinic composition of a high-performance piezoelectric a…

[Phys. Rev. B 93, 104103] Published Wed Mar 02, 2016

]]>Recent discoveries of supposedly pure $\alpha $-tetragonal boron require to revisit its structure. The system is also interesting with respect to a new type of geometrical frustration in elemental crystals, which was found in $\beta $-rhombohedral boron. Based on density functional theory calculations, the present…

[Phys. Rev. B 93, 104101] Published Tue Mar 01, 2016

]]>A new ice polymorph, called ice XVI, has recently been discovered experimentally by extracting the guest molecules from Ne hydrate. The ice and its filled form (clathrate hydrate) have a unique network topology which results in several interesting properties. Here we provide a theoretical method to …

[Phys. Rev. B 93, 054118] Published Mon Feb 29, 2016

]]>Recent advance in quantum simulations of interacting photons using superconducting circuits offers opportunities for investigating the Bose-Hubbard model in various geometries with hopping coefficients and self-interactions tuned to both signs. Here we investigate phenomena related to localized stat…

[Phys. Rev. B 93, 054116] Published Fri Feb 26, 2016

]]>Single-layer materials represent a new materials class with properties that are potentially transformative for applications in nanoelectronics and solar-energy harvesting. With the goal of discovering novel two-dimensional (2D) materials with unusual compositions and structures, we have developed a …

[Phys. Rev. B 93, 054117] Published Fri Feb 26, 2016

]]>The ferroelectric phase transition behavior in the highly ordered $\mathrm{Pb}\left(\mathrm{S}{\mathrm{c}}_{1/2}\mathrm{N}{\mathrm{b}}_{1/2}\right){\mathrm{O}}_{3}$ has been investigated by the dielectric and Brillouin spectroscopy. The dielectric permittivity ${\varepsilon}_{r}$ exhibits a sharp maximum without any frequency dispersion at its Curie temperature ${T}_{c}$. In the temperature range far ab…

[Phys. Rev. B 93, 054115] Published Thu Feb 25, 2016

]]>We develop a Ginzburg-Landau (GL) theory for fcc crystal-melt systems at equilibrium by employing two sets of order parameters that correspond to amplitudes of density waves of principal reciprocal lattice vectors and amplitudes of density waves of a second set of reciprocal lattice vectors. The cho…

[Phys. Rev. B 93, 054114] Published Wed Feb 24, 2016

]]>Crystal and electronic structures of $\mathrm{BiFe}{\mathrm{O}}_{3}$ thin films ($\sim 10$ and ∼300 nm) grown on $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrate have been investigated in terms of $\mathrm{BiFe}{\mathrm{O}}_{3}$ film thickness dependence using the advanced transmission electron microscopy (TEM) technique. Electron diffraction patterns of both $\mathrm{BiFe}{\mathrm{O}}_{3}$ thin films acquired…

[Phys. Rev. B 93, 064115] Published Wed Feb 24, 2016

]]>The motion of ferroelectric domain walls greatly contributes to the macroscopic dielectric and piezoelectric response of ferroelectric materials. The domain-wall motion through the ferroelectric material is, however, hindered by pinning on crystal defects, which substantially reduces these contribut…

[Phys. Rev. B 93, 064114] Published Tue Feb 23, 2016

]]>By combining DFT-based computational analysis and symmetry constraints in terms of group-subgroup relations, we analyzed the formation of the native crystalline structure of loellingite ${\mathrm{FeAs}}_{2}$. We showed that the ground state of the material exhibits the ordered patterns of the electronic localizatio…

[Phys. Rev. B 93, 064113] Published Mon Feb 22, 2016

]]>Ferroelectric transitions of a hexagonal multiferroic, $\mathrm{ErMn}{\mathrm{O}}_{3}$, are studied by x-ray scattering techniques. An isosymmetry transition, similar to that previously observed for $\mathrm{YMn}{\mathrm{O}}_{3}$, approximately 300 K below the well-known ferroic transition temperature, is investigated. The partially glassy behavior…

[Phys. Rev. B 93, 054113] Published Thu Feb 18, 2016

]]>In this paper, we propose a selective sampling procedure to preferentially evaluate a potential energy surface (PES) in a part of the configuration space governing a physical property of interest. The proposed sampling procedure is based on a machine-learning method called the *Gaussian process*, whic…

[Phys. Rev. B 93, 054112] Published Wed Feb 17, 2016

]]>