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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

]]>We develop statistical mechanical methods to predict the thermodynamic properties of dilute vacancies in multicomponent solids from first principles. The approach relies on a coarse-graining procedure to predict dilute vacancy concentrations with Monte Carlo simulations in alloys exhibiting varying …

[Phys. Rev. B 91, 224109] Published Wed Jun 24, 2015

]]>Branded for its potential electronic ferroelectricity, charge-ordered $\mathrm{LuF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ has a layered Fe triangular framework, whose topology is a source of degeneracy, both at the charge and spin levels. Here we present an in-depth characterization of $\mathrm{LuF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}\text{\u2212}hp$, the high-pressure $\left(hp\right)$ polymorph of $\mathrm{LuF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$, …

[Phys. Rev. B 91, 214111] Published Tue Jun 23, 2015

]]>Polar zinc titanate (ZnTiO${}_{3}$) is a promising lead-free ferroelectric compounds with high spontaneous polarization of 75 $\mu \phantom{\rule{0}{0ex}}C/c\phantom{\rule{0}{0ex}}{m}^{2}$, which is comparable with that of PbTiO${}_{3}$. In this work a collaboration of researchers from Germany, UK, and USA present a detailed investigation of vibrational properties of ZnTiO${}_{3}$ via the high-pressure Raman spectroscopy, second-harmonic generation, and $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations.

[Phys. Rev. B 91, 214110] Published Mon Jun 22, 2015

]]>Entropy barriers and aging states appear in martensitic structural-transition models, slowly re-equilibrating after temperature quenches, under Monte Carlo dynamics. Concepts from protein folding and aging harmonic oscillators turn out to be useful in understanding these nonequilibrium evolutions. W…

[Phys. Rev. B 91, 214108] Published Fri Jun 19, 2015

]]>Polarization reversal in ferroelectrics by the tip of a scanning probe microscope (SPM) has been intensively studied over the last two decades. In addition to classical domain formation and growth, a number of abnormal switching phenomena have been reported. In particular, it was experimentally and …

[Phys. Rev. B 91, 214109] Published Fri Jun 19, 2015

]]>Thermodynamic equilibrium in multicomponent solids subject to mechanical stresses is a complex nonlinear problem whose exact solution requires extensive computations. A few decades ago, Larché and Cahn proposed a linearized solution of the mechanochemical equilibrium problem by introducing the conce…

[Phys. Rev. B 91, 224107] Published Fri Jun 19, 2015

]]>Solid ${\mathrm{CS}}_{2}$ is superficially similar to ${\mathrm{CO}}_{2}$, with the same $Cmca$ molecular crystal structure at low pressures, which has suggested similar phases also at high pressures. We carried out an extensive first-principles evolutionary search in order to identify the zero-temperature lowest-enthalpy structures…

[Phys. Rev. B 91, 224108] Published Fri Jun 19, 2015

]]>We study point-defect diffusion in crystalline silicon using the kinetic activation-relaxation technique (k-ART), an off-lattice kinetic Monte Carlo method with on-the-fly catalog building capabilities based on the activation-relaxation technique (ART nouveau), coupled to the standard Stillinger-Web…

[Phys. Rev. B 91, 224106] Published Tue Jun 16, 2015

]]>The dynamical competition between the chemical mixing forced during energetic particle irradiation and thermally activated decomposition can lead to the stabilization of self-organized steady states in alloy systems comprised of immiscible elements. Continuum modeling and atomistic simulations predi…

[Phys. Rev. B 91, 214107] Published Mon Jun 15, 2015

]]>We study the entanglement spectrum of a translationally invariant lattice system under a random partition, implemented by choosing each site to be in one subsystem with probability $p\in [0,1]$. We apply this random partitioning to a translationally invariant (i.e., clean) topological state, and argue on…

[Phys. Rev. B 91, 220101(R)] Published Mon Jun 15, 2015

]]>Aluminum has been used prolifically as an impedance matching standard in the multimegabar regime (1 Mbar = 100 GPa), particularly in nuclear driven, early laser driven, and early magnetically driven flyer plate experiments. The accuracy of these impedance matching measurements depends upon the knowl…

[Phys. Rev. B 91, 224105] Published Mon Jun 15, 2015

]]>Static strain aging, a phenomenon caused by diffusion of solute atoms to dislocations, is an important contributor to the strength of substitutional alloys. Accurate modeling of this complex process requires both atomic spatial resolution and diffusional time scales, which is very challenging to ach…

[Phys. Rev. B 91, 224103] Published Fri Jun 12, 2015

]]>The exact mechanism responsible for the ferroelectricity in hexagonal manganite has been the subject of intense debate. Whether ferroelectricity and ferroelastic order appear at the same temperature and the role of covalency in the ferroelectric order are still discussed. High-temperature phase tran…

[Phys. Rev. B 91, 224104] Published Fri Jun 12, 2015

]]>Recent shock compression experiments produced clear evidence of a new carbon phase, but a full structural identification has remained elusive. Here we establish by *ab initio* calculations a body-centered cubic carbon phase in $Ia\overline{3}d\phantom{\rule{0.28em}{0ex}}\left({O}_{h}^{10}\right)$ symmetry, which contains twelve atoms in its primitive cell, th…

[Phys. Rev. B 91, 214106] Published Thu Jun 11, 2015

]]>We performed nuclear forward and inelastic scattering of synchrotron radiation by elemental Os utilizing the nuclear excited state of ${}^{187}\mathrm{Os}$ which is otherwise inaccessible using any practical radioactive decay process. The lifetime of the excited state, $3.06\left(8\right)\phantom{\rule{4.pt}{0ex}}\text{ns}$, and the energy of the transition, $\mathrm{9\dots}$

[Phys. Rev. B 91, 224102] Published Thu Jun 11, 2015

]]>Mn is used as a dopant to improve the electromechanical properties of perovskite oxides. We investigate the effects of Mn defects and associated vacancies on the electronic and atomic properties of ${\mathrm{BaTiO}}_{3}$. Using density functional theory (DFT) and $\mathrm{DFT}+U$ we investigate the equilibrium geometry and el…

[Phys. Rev. B 91, 214105] Published Tue Jun 09, 2015

]]>Searches for low-energy tetrahedral polymorphs of carbon and silicon have been performed using density functional theory computations and the *ab initio* random structure searching approach. Several of the hypothetical phases obtained in our searches have enthalpies that are lower or comparable to tho…

[Phys. Rev. B 91, 214104] Published Mon Jun 08, 2015

]]>We present an extended x-ray absorption fine structure study of the pyrochlore Y2Ru2O7 (8–298 K). We find evidence, on a local scale, of a significant magnetoelastic coupling at the Néel temperature TN∼77K pointed out by a huge Debye-Waller σ2 factor deviation from a correlated temperature dependent…

[Phys. Rev. B 91, 224101] Published Mon Jun 08, 2015

]]>At elevated temperatures, glasses crystallize via thermally activated diffusion. However, metallic glasses can also undergo deformation-induced crystallization at very low temperatures. Here we demonstrate the crystallization of $\mathrm{A}{\mathrm{l}}_{50}\mathrm{F}{\mathrm{e}}_{50}$ metallic glasses under cyclic deformation at 50 K using molecu…

[Phys. Rev. B 91, 214103] Published Fri Jun 05, 2015

]]>In this proof-of-concept analytical study (supported by numerical examples) the authors are able to achieve controllable enhancement of the electrostriction in a metamaterial medium consisting of an array of spheres in a host medium. Accounting for material dispersion and losses for a few test cases, they show a sizable enhancement (or suppression) and tunability of the electrostrictive properties. We anticipate that this study will open interesting directions previously unexplored in metamaterials research.

[Phys. Rev. B 91, 214102] Published Thu Jun 04, 2015

]]>(100)-epitaxial ${\mathrm{SrTiO}}_{3}$ thin films having biaxial compressive strains up to $-1.60\%$ were grown on lattice mismatched substrates. Two phase transitions induced by the coupled instabilities (antiferrodistortive and ferroelectric) in ${\mathrm{SrTiO}}_{3}$ were revealed in a common set of samples investigated at tempera…

[Phys. Rev. B 91, 214101] Published Wed Jun 03, 2015

]]>${\mathrm{BiMnO}}_{3}$ is the only transition-metal perovskite oxide that is insulating and shows strong ferromagnetism in bulk. This distinctive behavior would make it a promising candidate as a magnetoelectric multiferroic if it was also a polar material, but experiments have shown that bulk ${\mathrm{BiMnO}}_{3}$ has either a v…

[Phys. Rev. B 91, 184113] Published Thu May 28, 2015

]]>Structural stabilities of the Wadsley-type bronzes $\beta \text{\u2212}{\mathrm{Ag}}_{0.33}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$ and $\beta \text{\u2212}{\mathrm{Li}}_{0.33}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$ (both C2/m, *Z* = 6) have been studied with single-crystal x-ray diffraction in diamond anvil cells at room temperature to 8 and 13 GPa, respectively. $\beta \text{\u2212}{\mathrm{Ag}}_{0.33}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$ is stable at least to 8 GPa. $\beta \text{\u2212}{\mathrm{Li}}_{0.33}{\mathrm{V}}_{2}{\mathrm{O}}_{5}$ undergoes two p…

[Phys. Rev. B 91, 174113] Published Wed May 27, 2015

]]>${\mathrm{Sb}}_{2}{\mathrm{O}}_{3}$-based materials are of broad interest in materials science and industry. High-pressure study using diamond anvil cells shows promise in obtaining new crystal and electronic structures different from their pristine states. Here, we conducted *in situ* angle dispersive synchrotron x-ray-diffractio…

[Phys. Rev. B 91, 184112] Published Wed May 27, 2015

]]>We study experimentally the intermittent progress of the mechanically induced martensitic transformation in a Cu-Al-Be single crystal through a full-field measurement technique: the grid method. We utilize an in-house, specially designed gravity-based device, wherein a system controlled by water pum…

[Phys. Rev. B 91, 174111] Published Tue May 26, 2015

]]>By using first principles in combination with atomistic spin dynamics calculational methods, we determine the temperature-dependent free energies of the $L{2}_{1}$- and $L{1}_{0}-{\mathrm{Ni}}_{2}\left({\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_{x}\right)\text{Ga}\phantom{\rule{0.28em}{0ex}}\left(0\le x\le 1\right)$, including phonon vibrational and magnetic energies. The $x$-dependent martensitic phase transformation (MPT) tem…

[Phys. Rev. B 91, 174112] Published Tue May 26, 2015

]]>Using density functional theory calculations, many researchers have predicted that various tungsten nitride compounds ${\text{N}}_{1-x}{\text{W}}_{x}\left(x\frac{1}{2}\right)$ will be “ultraincompressible” or “superhard,” i.e., as hard as or harder than diamond. Necessary conditions for such compounds are that they have large bulk and shea…

[Phys. Rev. B 91, 184110] Published Tue May 26, 2015

]]>We propose a gravitational response theory for point defects (hedgehogs) binding Majorana zero modes in (3 + 1)-dimensional superconductors. Starting in 4 + 1 dimensions, where the point defect is extended into a line, a coupling of the bulk defect texture with the gravitational field is introduced.…

[Phys. Rev. B 91, 184111] Published Tue May 26, 2015

]]>Thermodynamic Ginzburg-Landau potential for temperature- and stress-induced phase transformations (PTs) between $n$ phases is developed. It describes each of the PTs with a single order parameter without an explicit constraint equation, which allows one to use an analytical solution to calibrate each …

[Phys. Rev. B 91, 174109] Published Thu May 21, 2015

]]>We studied solid solution effects on the mechanical properties of nanocrystalline (NC) ${\mathrm{Pd}}_{100-\mathrm{x}}{\mathrm{Au}}_{\mathrm{x}}$ alloys $(0\le x<50\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}\mathrm{at}.\%)$ at the low end of the nanoscale. Concentration has been used as control parameter to tune material properties (elastic moduli, Burgers vector, stacking fault energies) at basicall…

[Phys. Rev. B 91, 174110] Published Thu May 21, 2015

]]>We present a scaling theory for the entanglement spectrum under an external driving. Based on the static scaling of the Schmidt gap and the theory of finite-time scaling, we show that the Schmidt gap can signal the critical point and be used to estimate the critical exponents no matter in the finite…

[Phys. Rev. B 91, 184109] Published Thu May 21, 2015

]]>Vacancy properties in concentrated alloys continue to be of great interest because nowadays *ab initio* supercell simulations reach a scale where even defect properties in disordered alloys appear to be within reach. We show that vacancy properties cannot generally be extracted from supercell total en…

[Phys. Rev. B 91, 174107] Published Wed May 20, 2015

]]>We present a comprehensive study of polar and magnetic excitations in ${\mathrm{BiFeO}}_{3}$ ceramics and a thin film epitaxially grown on an orthorhombic (110) ${\mathrm{TbScO}}_{3}$ substrate. Infrared reflectivity spectroscopy was performed at temperatures from 5 to 900 K for the ceramics and below room temperature for the thin…

[Phys. Rev. B 91, 174108] Published Wed May 20, 2015

]]>The structure and stability of defect clusters in ${\mathrm{LiNbO}}_{3}$, as well as their influence on the linear and nonlinear optical susceptibilities, are calculated within density functional theory (DFT) using semilocal and hybrid exchange-correlation functionals. In particular, the complexes modeling the Li s…

[Phys. Rev. B 91, 174106] Published Tue May 19, 2015

]]>We present a detailed study of an electric-field-induced phase transition of a single layer of Fe on a Ni(111) substrate. Scanning tunneling microscopy at 4 K substrate temperature is used to provide the necessary electric field and to follow the transition from face-centered cubic to hexagonal clos…

[Phys. Rev. B 91, 184107] Published Tue May 19, 2015

]]>Canonical and microcanonical Monte Carlo simulations are carried out to study the electrocaloric effect (ECE) in ferroelectrics and relaxor ferroelectrics (RFEs) by direct computation of field-induced temperature variations at the ferroelectric-to-paraelectric phase transition and the nonergodic-to-…

[Phys. Rev. B 91, 184108] Published Tue May 19, 2015

]]>The $\alpha \text{-Fe}\leftrightarrow \epsilon \text{-Fe}$ pressure-induced transformation under pure hydrostatic static compression has been characterized with *in situ* x-ray diffraction using $\alpha \text{-Fe}$ single crystals as starting samples. The forward transition starts at 14.9 GPa, and the reverse at 12 GPa, with a width of $\alpha -\epsilon $ coexistence domain o…

[Phys. Rev. B 91, 174105] Published Thu May 14, 2015

]]>The coexistence pressure of two phases is a well-defined point at fixed temperature. In experiment, however, due to nonhydrostatic stresses and a stress-dependent potential energy barrier, different measurements yield different ranges of pressure with a hysteresis. Accounting for these effects, we p…

[Phys. Rev. B 91, 174104] Published Tue May 12, 2015

]]>We demonstrate experimentally the possibility of revealing fluctuations in the eigenfrequency of a resonator when the frequency noise is of the telegraph type. Using a resonantly driven micromechanical resonator, we show that the time-averaged vibration amplitude spectrum exhibits two peaks. They me…

[Phys. Rev. B 91, 174102] Published Mon May 11, 2015

]]>There are ample experimental evidences indicating that the ferroelastic domain walls of incipient ferroelectrics, such as $\mathrm{SrTi}{\mathrm{O}}_{3}$ and $\mathrm{CaTi}{\mathrm{O}}_{3}$, are polar. The emergence of such interfacial polar order at a domain wall is exciting and believed to arise from the coupling between a primary order parameter…

[Phys. Rev. B 91, 174103] Published Mon May 11, 2015

]]>Despite their structural similarities, ${\mathrm{SrBi}}_{2}{\mathrm{Ta}}_{2}{\mathrm{O}}_{9}$ (SBT) and ${\mathrm{SrBi}}_{2}{\mathrm{Nb}}_{2}{\mathrm{O}}_{9}$ (SBN) undergo a different sequence of phase transitions. The phase diagram of SBT as a function of the temperature includes an intermediate phase between the high-temperature phase and the ferroelectric ground state, while in the…

[Phys. Rev. B 91, 184106] Published Mon May 11, 2015

]]>We investigated the crystal and electronic structures of ferroelectric $\mathrm{B}{\mathrm{i}}_{4}\mathrm{T}{\mathrm{i}}_{3}{\mathrm{O}}_{12}$ single-crystalline thin films site-specifically substituted with $\mathrm{LaCo}{\mathrm{O}}_{3}$ (LCO). The epitaxial films were grown by pulsed laser epitaxy on $\mathrm{NdGa}{\mathrm{O}}_{3}$ and $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrates to vary the degree of strain. With increasing the LCO…

[Phys. Rev. B 91, 174101] Published Fri May 08, 2015

]]>Domain pattern variations with temperature were studied by polarizing light microscopy for the morphotropic phase boundary composition $0.67\mathrm{Pb}(\mathrm{M}{\mathrm{g}}_{1/3}\mathrm{N}{\mathrm{b}}_{2/3}){\mathrm{O}}_{3}-0.33\mathrm{PbTi}{\mathrm{O}}_{3}$ (PMN-0.33PT) single crystal. At room temperature, the monoclinic ${\mathrm{M}}_{\mathrm{A}}$ phase is the dominant phase in the unpoled crystal, which coexist…

[Phys. Rev. B 91, 184105] Published Fri May 08, 2015

]]>Solid-state amorphization of crystalline copper nanolayers embedded in a ${\mathrm{Cu}}_{64}{\mathrm{Zr}}_{36}$ metallic glass is studied by molecular dynamics simulations for different orientations of the crystalline layer. We show that solid-state amorphization is driven by a reduction of interface energy, which compensates th…

[Phys. Rev. B 91, 184103] Published Wed May 06, 2015

]]>We derive a method to determine the effective local elasticity tensor by combining the local stress, local strain, and global strain in conjunction with a linear least-squares solver. This method reduces to the standard stress-strain fluctuation method for the estimation of global moduli if the loca…

[Phys. Rev. B 91, 184104] Published Wed May 06, 2015

]]>The intergrowth crystal of $n$-tetracosane/urea presents a misfit parameter, defined by the ratio $\gamma ={c}_{h}/{c}_{g}({c}_{\mathrm{host}}/{c}_{\mathrm{guest}})$, that is very close to a commensurate value $(\gamma \cong 1/3)$. High-resolution diffraction studies presented here reveal an aperiodic misfit parameter of $\gamma =0.3369$, which is found to be constan…

[Phys. Rev. B 91, 184101] Published Tue May 05, 2015

]]>The stress fields of dislocations predicted by classical elasticity are known to be unrealistically large approaching the dislocation core, due to the singular nature of the theory. While in many cases this is remedied with the approximation of an effective core radius, inside which ad hoc regulariz…

[Phys. Rev. B 91, 184102] Published Tue May 05, 2015

]]>Understanding the ionic conduction in solid electrolytes in contact with electrodes is vitally important to many applications, such as lithium ion batteries. The problem is complex because both the internal properties of the materials (e.g., electronic structure) and the characteristics of the exter…

[Phys. Rev. B 91, 134116] Published Thu Apr 30, 2015

]]>Single crystal neutron diffraction is combined with synchrotron x-ray scattering to identify the different superlattice phases present in ${\text{Cs}}_{0.8}{\text{Fe}}_{1.6}{\text{Se}}_{2}$. A combination of single crystal refinements and first principles modeling are used to provide structural solutions for the $\sqrt{5}\times \sqrt{5}$ and $\sqrt{2}\times \sqrt{2}$ superlattice…

[Phys. Rev. B 91, 144114] Published Thu Apr 30, 2015

]]>Investigation of the wavelength dependence (725–1025 nm) of the threshold for nanosecond optical breakdown in water revealed steps consistent with breakdown initiation by multiphoton ionization, with an initiation energy of about 6.6 eV. This value is considerably smaller than the autoionization thr…

[Phys. Rev. B 91, 134114] Published Wed Apr 29, 2015

]]>Antiferroelectrics are under extensive reexamination owing to their unique properties and technological promise. Computationally, they pose a challenge for predictive modeling as they often do not possess well-defined localized electric moments and exhibit a delicate energetic balance between polar …

[Phys. Rev. B 91, 134112] Published Mon Apr 27, 2015

]]>The interaction of grain boundaries with ferroelectric domain walls strongly influences the extrinsic contribution to piezoelectric activity in $\mathrm{Pb}{\mathrm{Zr}}_{1-x},{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ (PZT), ubiquitous in modern transducers and actuators. However, the fundamental understanding of these phenomena has been limited by complex m…

[Phys. Rev. B 91, 134113] Published Mon Apr 27, 2015

]]>We employ first-principles calculations to study the atomic and electronic structure of various point defects such as vacancies, interstitials, and antisites in the stoichiometric as well as slightly off-stoichiometric ${\mathrm{Ti}}_{1-c}{\mathrm{C}}_{c}$ (including both C-poor and C-rich compositions, $0.49\le c\le 0.51$). The atomic …

[Phys. Rev. B 91, 134111] Published Fri Apr 24, 2015

]]>The high pressure structural and electronic evolution of bulk ${\mathrm{MoS}}_{2}$, an important transition metal layered dichalchogenide, is currently under active investigation, particularly in search of superconductivity. Recent theoretical and experimental work predicted and verified a $2{H}_{c}\to 2{H}_{a}$ layer sliding str…

[Phys. Rev. B 91, 144113] Published Thu Apr 23, 2015

]]>Mixtures of light elements with heavy elements are important in inertial confinement fusion. We explore the physics of molecular scale mixing through a validation study of equation of state (EOS) properties. Density functional theory molecular dynamics (DFT-MD) at elevated temperature and pressure i…

[Phys. Rev. B 91, 134109] Published Wed Apr 22, 2015

]]>Electron paramagnetic resonance (EPR) is used to identify a new and unique photoactive silicon-related point defect in single crystals of rutile $\mathrm{Ti}{\mathrm{O}}_{2}$. The importance of this defect lies in its assignment to interstitial silicon ions and the unexpected establishment of silicon impurities as a major h…

[Phys. Rev. B 91, 134110] Published Wed Apr 22, 2015

]]>Between 19 and 54 GPa, potassium has a complex composite incommensurate host-guest structure which undergoes two intraphase transitions over this pressure range. The temperature dependence of these host-guest phases is further complicated by the onset of an order-disorder transition in their guest c…

[Phys. Rev. B 91, 144111] Published Wed Apr 22, 2015

]]>The local atomic structure of the new nonmagnetic superconducting system ${\text{LaO}}_{1-x}{\text{F}}_{x}{\text{BiS}}_{2}$ is investigated using neutron diffraction and the pair density function analysis. Evidence for local charge fluctuations linked to a charge disproportionation of the Bi ions in the distorted lattice of superconduct…

[Phys. Rev. B 91, 144112] Published Wed Apr 22, 2015

]]>The high pressure-temperature behavior of titanium has been studied with x-ray diffraction in resistively heated and laser-heated diamond anvil cells up to 200 GPa and $\sim 3500$ K. The stability fields of $\alpha \text{\u2212}\mathrm{Ti},\omega \text{\u2212}\mathrm{Ti},\beta \text{\u2212}\mathrm{Ti},\gamma \text{\u2212}\mathrm{Ti}$, and $\delta \text{\u2212}\mathrm{Ti}$ have been determined in this range. $\gamma \text{\u2212}\mathrm{Ti}$ and $\delta \text{\u2212}\mathrm{Ti}$, which had been evi…

[Phys. Rev. B 91, 134108] Published Tue Apr 21, 2015

]]>The field-induced polarization reversal in the $c$-oriented ferroelectric phase of strained perovskite film has been studied. We show that in addition to the conventional longitudinal switching mechanism, when the $c$-oriented polarization vector changes its modulus, the longitudinal-transversal and tra…

[Phys. Rev. B 91, 144110] Published Tue Apr 21, 2015

]]>We report on theoretical and experimental investigation of $A$-site-driven ferroelectricity in ferromagnetic ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$ thin films grown on ${\mathrm{SrTiO}}_{3}$ substrates. Structural analysis and density-functional theory calculations show that epitaxial strain stretches the rhombohedral ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$ crystal lattice a…

[Phys. Rev. B 91, 134107] Published Mon Apr 20, 2015

]]>Inelastic scattering of electrons on crystals can excite lattice vibrations known as phonons. An energy resolution of 10 meV in the scattered electron energy loss has recently been demonstrated in scanning transmission electron microscopy (STEM), permitting experimenters to distinguish between elastic and inelastic scattering events. In this paper the authors present simulations showing that, with the recent improvement in energy resolution, atomic resolution phonon spectroscopy and imaging of crystals using STEM should now be feasible.

[Phys. Rev. B 91, 144108] Published Mon Apr 20, 2015

]]>We study the dynamics of inorganic antiferroelectric nanoclusters formed during an order-disorder transition and demonstrate the coexistence of the two phases in a region of 2–3 K around the transition temperature ${T}_{N}\sim 215$ K. Single crystals of ${\mathrm{NH}}_{4}{\mathrm{H}}_{2}{\mathrm{AsO}}_{4}$, a model hydrogen-bonded compound, show an anti…

[Phys. Rev. B 91, 140102(R)] Published Fri Apr 17, 2015

]]>The orientation-dependent equilibrium ferroelectric domain structures and dielectric properties of polydomain ${\mathrm{PbZr}}_{1}{}_{-}{}_{x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ thin films are investigated using a phenomenological Ginzburg-Landau-Devonshire thermodynamic model. We develop and describe three-dimensional polydomain models for (001)-, (101…

[Phys. Rev. B 91, 144106] Published Fri Apr 17, 2015

]]>We employ the quasiharmonic approximation to study the temperature-dependent lattice dynamics of the four different phases of cesium tin iodide $\left({\mathrm{CsSnI}}_{3}\right)$. Within this framework, we obtain the temperature dependence of a number of structural properties, including the cell volume, bulk modulus, and Grü…

[Phys. Rev. B 91, 144107] Published Fri Apr 17, 2015

]]>We demonstrate an innovative multifunctional artificial material that combines exotic metamaterial properties and the environmentally responsive nature of phase-change media. The tunable metamaterial is designed with the aid of two interwoven coordinate-transformation equations and implemented with …

[Phys. Rev. B 91, 134105] Published Thu Apr 16, 2015

]]>The origin of the relaxor behavior in ${\mathrm{K}}_{1-x}{\mathrm{Li}}_{x}{\mathrm{TaO}}_{3}\phantom{\rule{0.28em}{0ex}}\left(\mathrm{KLT}\right)$ and other disordered perovskites is now recognized to be due to the reorientation of the polar nanodomains formed by the correlated dipoles of off-center ions. The collective dynamics of these systems evolve through several temperature stages. O…

[Phys. Rev. B 91, 134106] Published Thu Apr 16, 2015

]]>We study a minimal model for a relaxor ferroelectric including dipolar interactions and short-range harmonic and anharmonic forces for the critical modes as in the theory of pure ferroelectrics together with quenched disorder coupled linearly to the critical modes. We present the simplest approximat…

[Phys. Rev. B 91, 144105] Published Tue Apr 14, 2015

]]>Using first-principles computational techniques, we have investigated the structural, vibrational, and dielectric properties of a Ruddlesden-Popper-type layered oxide ${\mathrm{Ba}}_{2}{\mathrm{ZrO}}_{4}$ subjected to a wide range of biaxial strains emulating epitaxial thin-film environment. Under compressive strains, this compo…

[Phys. Rev. B 91, 134103] Published Mon Apr 13, 2015

]]>The effect of octahedral tilting on the acentric structural transitions in $A\mathrm{Ga}{\mathrm{O}}_{3}/{A}^{\prime}\mathrm{Ga}{\mathrm{O}}_{3}$ [001], [110], and [111] superlattices $(A,{A}^{\prime}=\mathrm{La},\mathrm{Pr},\mathrm{Nd})$ is studied using density functional theory. We find the displacive transitions are driven by two octahedral rotations modes (${a}^{-}{a}^{-}{c}^{0}$ and ${a}^{0}{a}^{0}{c}^{+}$ tilting) with a…

[Phys. Rev. B 91, 134104] Published Mon Apr 13, 2015

]]>The interacting bosons in one-dimensional inversion-symmetric superlattices are investigated from the topological aspect. The complete phase diagram is obtained by an atomic-limit analysis and quantum Monte Carlo simulations and comprises three kinds of phases: superfluid, persisted charge-density-w…

[Phys. Rev. B 91, 134101] Published Fri Apr 10, 2015

]]>Metamaterial effective parameters may exhibit freedom from typical dispersion constraints. For instance, the emergence of a magnetic response in arrays of split ring resonators for long wavelengths cannot be attained in a passive continuous system obeying the Kramers-Kronig relations. We characteriz…

[Phys. Rev. B 91, 134102] Published Fri Apr 10, 2015

]]>Electric fields are generally known to favor the ferroelectric polar state over the antiferroelectric nonpolar state for their Coulomb interactions with dipoles in the crystal. In this paper, we directly image an electric-field-assisted ferroelectric-to-antiferroelectric phase transition during pola…

[Phys. Rev. B 91, 144104] Published Fri Apr 10, 2015

]]>Density functional theory calculations of the vibrational modes of ${\mathrm{Bi}}_{12}{\mathrm{SiO}}_{20}$ are presented, with a detailed assignment and geometry investigation of the vibrational modes in the sillenite structure. We show that the symmetry and geometry of the strong Raman peaks allow direct probing of the Bi-O(1) …

[Phys. Rev. B 91, 144103] Published Thu Apr 09, 2015

]]>We propose an approach to the problem of lattice distortions at low temperatures and ambient pressure in the solid hydrogens in their rotational ground states that explicitly accounts for the molecular nature of the constituent particles. The model is based on the idea that the second-order rotation…

[Phys. Rev. B 91, 144102] Published Wed Apr 08, 2015

]]>Series of high-pressure x-ray diffraction patterns of iron and its high-pressure polymorphs were collected with 0.1–0.2-s exposure time utilizing a membrane diamond anvil cell (DAC) for compression at various loading and unloading rates to a maximum pressure of 70 GPa. Strain rates of ${10}^{-2}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{-1}$ at a m…

[Phys. Rev. B 91, 144101] Published Tue Apr 07, 2015

]]>Synchrotron-radiation-based Mössbauer absorption spectroscopy of ${}^{40}\mathrm{K}$ nuclei was performed. We investigated potassium nanoclusters arrayed in a porous crystal of sodalite. The nanoclusters exhibit antiferromagnetic (AFM) ordering below $\simeq 72$ K. The energy-domain ${}^{40}\mathrm{K}$ Mössbauer spectra were successfully …

[Phys. Rev. B 91, 140101(R)] Published Mon Apr 06, 2015

]]>We report the results of pressure-induced phase transitions and metallization in ${\mathrm{VO}}_{2}$ based on synchrotron x-ray diffraction, electrical resistivity, and Raman spectroscopy. Our isothermal compression experiments at room temperature and 383 K show that the room temperature monoclinic phase $(M1,\phantom{\rule{0.16em}{0ex}}P{2}_{1}/c)$…

[Phys. Rev. B 91, 104110] Published Tue Mar 31, 2015

]]>The pressure-induced phase transition of the multiferroic manganese tungstate ${\mathrm{MnWO}}_{4}$ is studied on single crystals using synchrotron x-ray diffraction and Raman spectroscopy. We observe the monoclinic $P2/c$ to triclinic $P\overline{1}$ phase transition at 20.1 GPa and get insight on the phase transition mechanism…

[Phys. Rev. B 91, 104109] Published Mon Mar 30, 2015

]]>Relaxor-based ferroelectrics have been known for decades to possess a relatively thick surface layer (“skin”) that is distinct from its interior. Yet while there is consensus about its existence, there are controversies about its symmetry, phase stability, and origin. In an attempt to clarify these …

[Phys. Rev. B 91, 094111] Published Thu Mar 26, 2015

]]>Chiral crystals come in left- and right-handed forms. Methods for using electron diffraction to determine crystal chirality have heretofore required the use of multiple scattering and depended sensitively on the sample thickness. Here it is shown that these constraints can be removed with the use of electron vortex beams (which carry orbital angular momentum) in a transmission electron microscope. In accordance with theoretical expectation, the chirality of a sample of Mn${}_{2}$Sb${}_{2}$O${}_{7}$ is experimentally determined.

[Phys. Rev. B 91, 094112] Published Thu Mar 26, 2015

]]>${\mathrm{Th}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Ge}}_{13}$ and ${\mathrm{U}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Ge}}_{13}$ crystallize with primitive cubic ${\mathrm{Tm}}_{3}{\mathrm{Co}}_{4}{\mathrm{Ge}}_{13}$ and noncentrosymmetric rhombohedral ${\text{HT-Y}}_{3}{\mathrm{Pt}}_{4}{\mathrm{Ge}}_{13}$ type of structures, respectively, which are derivatives of the cubic ${\mathrm{Yb}}_{3}{\mathrm{Rh}}_{4}{\mathrm{Sn}}_{13}$ prototype. Measurements of magnetic susceptibility, electrical resistivity, specific heat, thermopower…

[Phys. Rev. B 91, 094110] Published Wed Mar 18, 2015

]]>Iron doped ${\text{LiNbO}}_{3}$ crystals with different iron valence states are investigated. An extended x-ray absorption fine structure (EXAFS) spectroscopy study highlights evident changes in the local structure around iron that can be ascribed to the presence of small polarons. In particular, when a ${\text{Fe}}^{3+}$ repl…

[Phys. Rev. B 91, 094109] Published Tue Mar 17, 2015

]]>A roadblock in utilizing III-V semiconductors for scaled-down electronic devices is their poor dopant activation. As a first step to unravel the dopant behavior in InGaAs, we studied the tendency for dopant formation computationally using two approaches: *ab initio* and semiempirical methods. We studi…

[Phys. Rev. B 91, 094108] Published Mon Mar 16, 2015

]]>The diffusionless pseudobinary phase diagram, monodomain properties, and free energy of $(1-x)\mathrm{Ba}(\mathrm{Z}{\mathrm{r}}_{0.2}\mathrm{T}{\mathrm{i}}_{0.8}){\mathrm{O}}_{3}\text{\u2212}x\left(\mathrm{B}{\mathrm{a}}_{0.7}\mathrm{C}{\mathrm{a}}_{0.3}\right)\mathrm{Ti}{\mathrm{O}}_{3}$ are computed for comparison with experimental results. Specifically, the variation of the spontaneous polarization, anisotropy energy, and free energy with respect to tempe…

[Phys. Rev. B 91, 104108] Published Mon Mar 16, 2015

]]>We have performed *ab initio* band-structure calculations on more than 2000 half-Heusler compounds in order to search for new candidates for topological insulators. Herein, LiAuS and NaAuS are found to be the strongest topological insulators with the bulk band gaps of 0.20 and 0.19 eV, respectively, d…

[Phys. Rev. B 91, 094107] Published Thu Mar 12, 2015

]]>Using all-atom molecular dynamics (MD) simulations, we have studied the mechanical properties of ZnS/CdS core/shell nanowires. Our results show that the coating of a few-atomic-layer CdS shell on the ZnS nanowire leads to a significant change in the stiffness of the core/shell nanowires compared to …

[Phys. Rev. B 91, 104107] Published Thu Mar 12, 2015

]]>The atomistic study of kink pairs on screw dislocations in body-centered cubic (bcc) metals is challenging because interatomic potentials in bcc metals still lack accuracy and kink pairs require too many atoms to be modeled by first principles. Here, we circumvent this difficulty using a one-dimensi…

[Phys. Rev. B 91, 094105] Published Mon Mar 09, 2015

]]>We propose a method to evaluate the diffusion coefficient of vacancy-hydrogen clusters (${\mathrm{VH}}_{n})$ in metals. The key is a good separation of time scales between H diffusion and the metal-vacancy exchange. The Ni-H system is investigated in details, using *ab initio* calculations, but the arguments can be t…

[Phys. Rev. B 91, 094106] Published Mon Mar 09, 2015

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