Polarized Raman scattering investigations of the ir OH stretch mode vibration have been performed in a variety of prototype oxidic crystals, ${\mathrm{KTaO}}_3$, ${\mathrm{SrTiO}}_3$, ${\mathrm{K}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Li}}_{\mathit{x}}$${\mathrm{TaO}}_3$, ${\mathrm{TiO}}_2$, ${\mathrm{LiTaO}}_3$, with the aim of providing information on the sites of the incorporation of hydrogen. The traditionally used polarized ir absorption is limited by ensemble averages and its lacking sensitivity to crystallographic orientations of defects. Contrarily Raman scattering is sensitive to the symmetry of the dynamical mode. The problem of extracting information on a single defect from an ensemble is treated in the behavior-type theory, which has been developed recently for defects in cubic crystals and was extended to tetragonal and trigonal crystals in the course of these investigations. The principles of the method and the extensive tables are summarized. We describe an experimental method for determining the precise optical alignment of the scattering geometry. In the cubic phase of the perovskites ${\mathrm{SrTiO}}_3$ and ${\mathrm{KTaO}}_3$ with isotropic ir absorption, the Raman data allow us to reject one out of three models, where the protons vibrate between the two next-nearest oxygen ions along the cubic axes, by excluding the related ${\mathit{C}}_2$[100] symmetry.

In tetragonal ${\mathrm{SrTiO}}_3$ the absorption band splits into three components. In the second model the protons vibrate between the ${\mathrm{O}}^{2\mathrm{-}}$ and the ${\mathrm{Sr}}^{2+}$ ions on the face diagonal of the cube, in the last along the edges of the oxygen octahedron between the two nearest-neighbor oxygen ions. The second model can be rejected, because the claimed vertical mirror plane σ(010) is not observed in the Raman spectra. The third model claims no mirror symmetry because of the tilting of the octahedra. In ${\mathrm{K}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Li}}_{\mathit{x}}$${\mathrm{TaO}}_3$, x=0.023, a polar tetragonal phase occurs due to the off-center freezing of the ${\mathrm{Li}}_{\mathit{K}}$ ions along the polar axis. Again three subbands of the OH mode occur. But the bands, which reflected the breakdown of the σ(010) symmetry in ${\mathrm{SrTiO}}_3$, do not occur in ${\mathrm{K}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Li}}_{\mathit{x}}$${\mathrm{TaO}}_3$. The observed vertical mirror plane σ(010) reflects the nontilted arrangement of the octahedra in ${\mathrm{K}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Li}}_{\mathit{x}}$${\mathrm{TaO}}_3$. In ${\mathrm{TiO}}_2$ (rutile) the Raman data reveal a ${\mathit{C}}_{1\mathit{h}}$(001) symmetry for the prominent OH stretch mode. This firmly establishes the model, where the protons vibrate in the center of the open channels between the next-nearest ${\mathrm{O}}^{2\mathrm{-}}$ ions in the basal plane. In trigonal ${\mathrm{LiTaO}}_3$ the crystal symmetry is so low that hardly any models can be discriminated on the basis of their symmetry, because most of them deal with ${\mathit{C}}_1$ symmetry. This is detected in the experiment and thus any orientation not along the trigonal axis or the vertical mirror plane is compatible with this result. Still one model proposed for ${\mathrm{LiNbO}}_3$ can be excluded.

Measurements of light-scattering spectra from rutile structure fluorides using circularly polarized incident light have revealed vibrational Raman and Rayleigh optical activity when the incident light is tilted away from the crystal c-axis direction. This activity is shown to arise from the depolarizing effect of the crystal birefringence on the incident light.

Defect-induced one-phonon absorption of far-infrared radiation is utilized to generate a nonequilibrium phonon population in ${\mathrm{PrF}}_3$. We observe that the nonequilibrium phonon population stimulates energy transfer between the ${\mathit{A}}_3$ and the stoichiometric sites of the ${\mathrm{Pr}}^{3+}$ ion. We investigate both the spectral and temporal dynamics associated with this process and compare the data to a simple rate-equation model. An upper limit of (1.9±0.2)×${10}^6$ ${\mathrm{s}}^{\mathrm{-}1}$ for the ${\mathit{A}}_3$ main-site transfer rate is determined.

A model is discussed in which a solid is simulated by a quantum-mechanical molecular cluster of atoms embedded in a classical atomistic crystal. An effective crystal Hamiltonian is derived, based on adiabatic and harmonic approximations. The relationship is demonstrated between the cluster state and perfect crystal equilibrium configuration and force constants. Similarly, when an impurity is introduced, the relationship is found between the cluster state and the linear and quadratic impurity-phonon coupling coefficients. Also, the effective potential is found for the quantum-mechanical treatment of a light impurity not subject to the harmonic approximation. The distortion field and force constants of the defect crystal containing the impurity are discussed. The results are related to practical methods of computation. The relationship of this work to the problem of quantum diffusion of muonium in alkali halides is described.

The confined-oscillator scaling model gives the stretching frequencies ${\nu }_0$ of isolated ${\mathrm{CN}}^{\mathrm{-}}$ impurities in alkali halide and silver halide crystals and ${\nu }_3$ of ${\mathrm{CN}}^{\mathrm{-}}$ molecules sandwiched between satellite impurity cations in terms of (1) the kind of neighbor-ion species, (2) the axial space availability, and (3) the position of neighbor ions relative to the host lattice.

The movement of dislocations in response to a finite-amplitude shear stress is treated as a quantum-mechanical process in which the dislocations tunnel through the lattice potential barriers and transit into adjacent potential wells. For simple potential barriers, the predicted dislocation velocity and macroscopic plastic strain rate contain all of the essential features observed in shock and impact experiments. Insights are provided into electroplastic effects and into a possible microscopic mechanism of crystal failure.

The macroscopic diffusion coefficient, obtained in an ideal pulsed-field-gradient spin-echo (PFGSE) experiment in the long-time limit, should exactly equal that derived from the electrical conductivity only when the surface relaxivity ρ and surface electrical conductivity vanish. In general, the coefficient derived by PFGSE techniques can be either greater or less than its electrical counterpart, depending on the pore geometry and other factors. Formally, the effect of ρ can be seen from the structure of a perturbation expansion based on the ρ=0 time-dependent solutions of the pore-space diffusion problem. In addition, analytic results for periodic structures with partially absorbing boundary conditions and numerical simulations are used to illustrate the differences between the diffusion coefficients for ρ=0 and ρ≠0. In treating disordered media, our simulations are limited to systems that are not heterogeneous beyond the PFGSE diffusion length scale.

Natural polycrystalline graphite was compressed using a 6-8-type multianvil and a Drickamer cell, and the recovered samples were examined by x-ray diffraction and transmission-electron microscopy. Diamond was formed in the samples from 14∼20 GPa and 800∼1200 °C generated by the multianvil. These P-T conditions are included in the region where the formation of hexagonal diamond was reported by Bundy and Kasper. Hexagonal diamond was not apparent in any of the recovered samples. Instead, the formation of n-diamond, which is a new carbon phase recently identified in a shock-wave study, by static compression was confirmed in the samples from 40 GPa, 25 °C and 14 GPa, 1200 °C.

Crystals of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ contain vacancies that move around by a quantum-mechanical hopping process. The density and pressure of these vacancies can be experimentally studied. The accuracy of the experiments is high enough to detect the effect of the Bose statistics of the vacancies. In this paper we examine the effect of the hard-core repulsion between the vacancies, which should also have a measurable effect on their behavior. We set up a virial expansion for a lattice gas of hard-core particles, and calculate the second virial coefficient. It turns out that the vacancies behave as ideal Bose particles at low temperatures, but that the hard-core interaction makes them behave more and more like fermions as the temperature increases.

The long-wavelength phonon spectrum of an alternating chain, consisting of molecules with internal degrees of freedom and ions (atoms) in between is investigated within a frozen-phonon-type approach for the period-4 mixed charge-density-wave–bond-order-wave (CDW-BOW) ground state of a one-dimensional Hamiltonian with 3/4-filled bands, diagonal, and off-diagonal electron-phonon interaction. Raman and infrared data of the recently synthesized quasi-one-dimensional system ${\mathrm{Ca}}_{1.8}$${\mathrm{Sr}}_{0.2}$${\mathrm{CuO}}_3$ are analyzed within this model. The occurrence of ‘‘forbidden’’ Raman modes is explained semiquantitatively as the consequence of the period-4 CDW-BOW ground state. The parameters derived from the experimental data are consistent with intermediately strong electron-electron interaction. Necessary experiments to check the relevance of the proposed model are discussed.

The critical behavior of charge-density waves (CDWs) in the pinned phase is studied for applied fields increasing toward the threshold field, using recently developed renormalization-group techniques and simulations of automaton models. Despite the existence of many metastable states in the pinned state of the CDW, the renormalization-group treatment can be used successfully to find the divergences in the polarization and the correlation length, and, to first order in an ε=4-d expansion, the diverging time scale. The automaton models studied are a charge-density wave model and a ‘‘sandpile’’ model with periodic boundary conditions; these models are found to have the same critical behavior, associated with diverging avalanche sizes. The numerical results for the polarization and the diverging length and time scales in dimensions d=2,3 are in agreement with the analytical treatment. These results clarify the connections between the behavior above and below threshold: the characteristic correlation lengths on both sides of the transition diverge with different exponents. The scaling of the distribution of avalanches on the approach to threshold is found to be different for automaton and continuous-variable models.

Measurements of the thermal diffusivities between 80 and 500 K for five silicate glasses of composition 0.15(${\mathit{M}}_2$O)0.05(ZnO)0.05(BaO)0.05(${\mathrm{Eu}}_2$${\mathrm{O}}_3$)0.70(${\mathrm{SiO}}_2$), where M is Li, Na, K, Rb, or Cs are presented. In each case the thermal diffusivity asymptotically approaches a linear temperature dependence at high temperatures. The data are analyzed using a model that contains extended phonons and, above a mobility edge, localized phonons that participate in the transport through thermally activated hopping. The lowest-frequency Raman peak is used as a quantitative measure of the mobility edge. The thermally averaged relaxation times that characterize the localized-mode and extended-mode contributions to the thermal diffusivities are studied as functions of the mobility edge across this isostructural series of glasses.

In this paper we present measurements of the thermal diffusivities of five glasses between 100 and 500 K. These glasses have composition 0.15(${\mathrm{Na}}_2$O)0.15(MO)0.05(${\mathrm{Eu}}_2$${\mathrm{O}}_3$)0.65(${\mathrm{SiO}}_2$), where M is a divalent network modifier Mg, Ca, Sr, Ba, or Zn. The thermal transport is represented by a two-carrier model of conventional phonon-gas transport by extended phonons and thermally activated hopping of phonons whose eigenvectors are localized in the disordered network of the glass. The later contribution is required to explain the increase in the thermal diffusivity at temperatures above room temperature. The extended phonons produce a transport that is a decreasing function of temperature between 100 and 250 K in these glasses. Using the boson peak from Raman scattering as a measure of the phonon mobility edge, agreement with the temperature and frequency dependence of the two-localized-one-extended-phonon anharmonic process studied by Jagannathan et al. is obtained for both the localized and the extended phonons. The model is also applied to fused silica to account for results between 100 and 1100 K, with the modification that the limiting process for the extended states does not explicitly depend on temperature.

X-band electron-paramagnetic-resonance measurements have been carried out on ${\mathrm{VO}}^{2+}$-doped single crystals of [${\mathrm{NH}}_3$(${\mathrm{CH}}_2$)${\mathrm{NH}}_3$] ${\mathrm{ZrF}}_6$ at room temperature. Superhyperfine structure due to ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$ has been observed in abundance in the spectra recorded at all orientations. There are two occupation sites for ${\mathrm{VO}}^{2+}$, both interstitial, in the triclinic cell.

Electronic specific heat due to virtual excitation of the crystal-field singlet ground state is studied by including higher-order processes, following the Doniach-Engelsberg-Brinkman theory. As the effective electron-electron interaction mediated by the excitation of the crystal-field states turns repulsive near the Fermi surface, correspondence with the Hubbard model is investigated. The specific heat is separated into a fermionlike term and a bosonlike term. The former has a T-linear contribution which corresponds to that in the Hubbard model. The bosonlike term corrects the Schottky-type contribution of individual crystal-field states by their collective modes. Numerical calculation is made in a simplified model for real substances to see the relative size of the fermion and boson terms in a magnetic field.

The spectroscopic properties of octahedrally coordinated ${\mathrm{Ni}}^{2+}$ ions in ${\mathrm{Gd}}_3$${\mathrm{Ga}}_5$${\mathrm{O}}_{12}$ garnet are described with a five-parameter model in the framework of the adiabatic approximation. The effect of spin-orbit coupling on the vibronic potentials due to the fully symmetric vibration is pointed out. Values of parameters useful for comparison with previous works, such as a pseudo-Huang-Rhys parameter or the ‘‘phonon’’ energies of the levels, are given.

We present self-consistent spin-polarized electronic-structure calculations for amorphous ${\mathrm{Fe}}_{\mathit{x}}$${\mathrm{B}}_{100\mathrm{-}\mathit{x}}$ (50≤x≤95) alloys, based on a supercell linear-muffin-tin-orbital technique and realistic structure models produced by molecular-dynamics simulations. We show that the electronic densities of states of the amorphous alloys are very similar to that of the crystalline Fe borides. This confirms the conclusions as to the similarity of the local order in the crystalline and amorphous phases drawn on the basis of the structural studies. The calculated composition dependence of the magnetic moments is in good agreement with experimental data on amorphous films, with a maximum of the magnetic moment close to 15 at. % B. The decrease of the moment for lower B content is shown to arise from the competition between ferro- and antiferromagnetic exchange interactions, the decrease with higher B content is due to a dilution effect: polarizable d-d bonds are replaced by magnetically inert p-d bonds. We also present detailed calculations of the photoemission intensities.

This paper is devoted to a theoretical study of the magnetic properties of Fe/Pd superlattices. We mostly focus our attention on the determination of both the interlayer magnetic couplings (IMC) and the magnetic-moment distributions as a function of the Pd spacer’s thickness. We use an ab initio method (augmented spherical wave) to determine self-consistently the electronic structure, the magnetic-moment distributions, and the total energies for the considered systems. We consider two model structures for the Pd spacers (1) a fct structure for which the Pd atoms keep their bulk atomic volume and (2) a fcc structure for which the Pd atomic volume is expanded. For the first structure, the magnetic polarization in the palladium spacer is limited mostly to the first three monolayers near the Fe-Pd interfaces and the IMC are similar to the ones obtained for nonmagnetic spacers. The IMC decrease rapidly with an oscillating behavior. On the contrary, for the second atomic structure, the whole Pd spacer is polarized with a moment of about 0.15${\mathrm{\mu }}_{\mathit{B}}$/atom for n≤14 (n being the number of Pd atomic layers) and the IMC are ferromagnetic in a large range of Pd thicknesses. We present a detailed study of (i) ${\mathrm{Fe}}_3$${\mathrm{Pd}}_1$ superlattices whose ground state is shown to be antiferromagnetic and (ii) the polarization induced in the Pd spacer in relation with the current theoretical models.

The magnetic properties of undoped and Li-doped ${\mathrm{MgCu}}_2$${\mathrm{O}}_3$ single crystals have been studied by magnetic-susceptibility and neutron-diffraction measurements. The pure compound is a semiconductor with an antiferromagnetic ground state (${\mathit{T}}_{\mathit{N}}$=95 K). Above ${\mathit{T}}_{\mathit{N}}$, short-range magnetic correlations within the Cu-O chains of the ${\mathrm{MgCu}}_2$${\mathrm{O}}_3$ structure give rise to a predominantly one-dimensional (1D) magnetic behavior. This is revealed by the quantitative interpretation of the susceptibility measurements. Below ${\mathit{T}}_{\mathit{N}}$, the 3D magnetic structure, derived from neutron-diffraction experiments, can be described by an essentially collinear model. A small spin canting, however, exists, because adjacent ${\mathrm{CuO}}_6$ octahedra are strongly tilted with respect to each other. The magnetic structure can be decomposed into two independent magnetic sublattices, which, in the mean-field approximation, are not coupled. The topology is similar to the one producing an infinitely degenerate state in antiferromagnetic fcc lattices. Doping experiments with Li clearly demonstrate the importance of spin fluctuations and fluctuations of the local exchange fields for lifting the degeneracy in such a system. A remarkably small amount of Li (about 2 mole % Li) is sufficient to disturb the magnetic lattice in such a way that the almost collinear spin arrangement changes into an arrangement where the spins of one sublattice are strongly canted with respect to the spins of the other sublattice.

Perturbed-angular-correlation (PAC) spectroscopy was used to measure nuclear-electric-quadrupole interactions in the orthorhombically-distorted perovskites ${\mathrm{SrRuO}}_3$ and ${\mathrm{CaRuO}}_3$ over temperatures ranging from laboratory to very high temperatures. At 77 K, PAC spectroscopy was used to measure combined electric-quadrupole and magnetic-dipole interactions in magnetically ordered ${\mathrm{SrRuO}}_3$ and pure electric-quadrupole interactions in paramagnetic ${\mathrm{CaRuO}}_3$. The ${}_{}{}^{111}{}_{}{}^{}\to _{}^{111}{}_{}{}^{}$Cd PAC probe was used for these measurements, and it substituted into the Ru site in ${\mathrm{SrRuO}}_3$ and very likely into the Ru site in ${\mathrm{CaRuO}}_3$. The temperature dependence of the electric-field-gradient (EFG) parameters for ${\mathrm{SrRuO}}_3$ indicates the onset of a structural phase transition at approximately 800 K. The presence of this transition indicates that the laboratory-temperature structure of ${\mathrm{SrRuO}}_3$ has lower-than-cubic symmetry. At very high temperatures >1600 K, the structure of ${\mathrm{CaRuO}}_3$, as given by the EFG parameters, becomes very similar to the laboratory-temperature structure of ${\mathrm{SrRuO}}_3$. At 77 K in ${\mathrm{SrRuO}}_3$, the measured Ru-site supertransferred hyperfine field is 39±3 kOe. Using ${}_{}{}^{99}{}_{}{}^{}\mathrm{Ru}$ and ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer-effect information and other ${}_{}{}^{111}{}_{}{}^{}\to _{}^{111}{}_{}{}^{}$Cd PAC measurements, the magnetic hyperfine fields at the Ru site in ${\mathrm{SrRuO}}_3$ and at the Fe site in ${\mathrm{PrFeO}}_3$ are compared.