Angle-dispersive powder-diffraction techniques using an image-plate area detector have been used to study the high-pressure phases of CdTe to 5 GPa. The recently discovered cinnabar phase between the zinc-blende and NaCl phases is found to be stable on both pressure increase and decrease. No pressure range of single-phase cinnabar has been found on pressure increase, but a single phase is obtained on pressure decrease, between 3.6 and 2.7 GPa. The cinnabar phase has an average bulk modulus of 32(1) GPa and is significantly more compressible than the zinc-blende and NaCl phases. All three phases are site ordered. Each atom in the cinnabar structure has two nearest-neighbor distances of ∼2.74 Å (a bonds) and two of ∼2.94 Å (b bonds), and the structure is thus close to fourfold coordinated. The next-nearest-neighbor distances are two of ∼3.5 Å (c bonds). The a bonds are very similar in length to the nearest-neighbor distance in the zinc-blende phase, and the b bonds increase with pressure towards the nearest-neighbor distance in the NaCl phase. The c-bond distance and the interbond angles also become closer to the geometry of the NaCl structure with increasing pressure, but there are still large discontinuities in bond lengths and angles at the cinnabar-to-NaCl transition.

A gradual increase of disorder with temperature in the lithium subsystem is observed for the superionic conductor ${\mathrm{Li}}_3$${\mathrm{Fe}}_2$(${\mathrm{PO}}_4$${)}_3$ for a rise from 470 K to 820 K. Structural phase transitions occurring in this temperature interval result in a continuous way in changes of the activation energy of the disordering. It differs from the abrupt disordering of the conductive ion subsystem in the vicinity of the structural phase transition, which is the usual case for the superionics. This behavior is explained within a two-level phenomenological model that assumes weak ion-ion interaction in the lithium subsystem and a population of the excited state due only to the temperature increase.

The emission spectra of KBr and KCl were obtained in the temperature range 18–290 K during the thermoluminescence (TL) measurements and 40–300 K during the cathodoluminescence (CL) measurements. The 400–600 nm broad emission bands in KBr and KCl at low temperatures are resolved into at least two components: the self-trapped-exciton (STE) π emission and the α-center emission by using different modulation frequencies in the CL work. This separation of component bands is supported by the TL measurements. The different temperature dependences of the STE emission in the CL and TL cases and the 50–90 K decay processes of the CL STE bands are discussed. The relation between the F-band self-absorption in KCl and the irradiation dose is also discussed.

A quantitative physical model is presented for the breakdown of solids by void or channel discharges. It is found that fractal treelike structures only occur when the ‘‘fields’’ at the growth tips are allowed to fluctuate about their Laplace values. By treating the local-field enhancement factor as a white noise produced by the breakdown mechanism itself, it is shown that the amount of branching depends only on the range of fluctuations allowed.

We have studied the crystal structures of Ti, Zr, and Hf under pressure by means of first-principles, total-energy calculations. The three metals are shown to exhibit a crystal structure sequence hcp→ω→bcc, with increasing pressure. This is in good agreement with experiment for Zr and Hf, whereas the bcc structure for Ti is a prediction. The calculated transition volumes as well as transition pressures compare fairly well with experiment. Also, the computed c/a ratio for hcp Ti, Zr, and Hf is found to be in good agreement with experiment. Similarly the calculated c/a ratio for Zr in the ω structure agrees well with measurement. The chemical bonding of the ω structure is shown to be quite different from what is normally the case in the transition metals, with a large degree of covalency. A search for the ω structure in Tc and Ru was fruitless yielding a stable hcp structure. At zero temperature and zero pressure the bcc crystal structure is found to be mechanically unstable for Ti, Zr, and Hf.

Results of electronic-structure calculations on the experimentally observed low-temperature monoclinic α phase of Pu are presented and compared to calculations for fcc (δ phase) and fictitious hexagonal Pu. Energy-volume curves for fcc and hexagonal phases of Pu reveal a tendency towards more open structures, primarily due to an increased occupation of the 6d band, which has a strongly itinerant character. Bonding in these structures is not dominated by the 5f band. However, in the experimental α phase, which is computed to be the most stable, the arrangement of the atoms in the unit cell is such that 5f bonding is strongly enhanced when compared with fcc and hexagonal Pu. In addition the α-Pu structure benefits from a substantial charge transfer from itinerant 7s states to the bonding 6d states. A relative downward shift of the 5f band reduces the width of the valence band in α-Pu. The predicted narrowing should be observable in photoemission experiments on α- and δ-Pu.

We report the simulation of the optical absorption and emission spectra of the ${\mathrm{Eu}}^{3+}$ ion doped in a sodium disilicate glass. A model of this glass was previously simulated by the molecular-dynamics technique. We employ a full treatment, including J mixing, of the point-charge crystal-field method developed for doped crystalline materials in order to simulate (1) the ${}_{}{}^5{}_{}{}^{}$${\mathit{L}}_6$${,}^5$${\mathit{D}}_{3,2,1,0}$${\leftarrow }^7$${\mathit{F}}_{0,1}$ absorption spectrum and (2) the ${}_{}{}^5{}_{}{}^{}$${\mathit{D}}_0$${\to }^7$${\mathit{F}}_{0–6}$ emission spectrum of the ${\mathrm{Eu}}^{3+}$ ion. This produces simulated spectra with correct energies and relative intensities. A comparsion to experimental room-temperature absorption and fluorescence spectra of the corresponding laboratory glass is presented. By combining the simulated structural model with the calculated optical spectra, we are able to investigate spectra-structure correlations of doped inorganic glasses.

The short- and medium-range orders of ${\mathrm{GeSe}}_2$ chalcogenide glass were studied by using the radial distribution function. The effect of the annealing temperature on the short-range order structure of this glass was investigated. The short-range order structure of as-prepared and annealed ${\mathrm{GeSe}}_2$ chalcogenide glass is regular tetrahedron (edge and corner sharing ${\mathrm{GeSe}}_4$ tetrahedra). The medium-range order of the ${\mathrm{GeSe}}_2$ chalcogenide glass is chemical order associated with topological order. The topological structure of the medium-range order can be described by the Phillips model. The basic structure unit does not change after annealing. Most changes observed in the diffraction patterns may be interpreted in the framework of structural relaxation during which a system tends to attain a metastable equilibrium state. This relaxation can be described by an α process.

The low-temperature phase diagram of a lattice model, proposed for studying the micellar binary solutions of water and amphiphile, is investigated.

We work out a theory of low-energy Raman scattering in glasses. The scattering and the energy transfer are due to interaction of the light with the soft potentials in glasses. We exploit relations between the scattering cross sections at a certain energy transfer, ħω, and the mean free paths of sound and electromagnetic radiation for the frequency ω. A comparison between the theory and experiment is made. An explanation of the boson peak is proposed. We come to a conclusion that the peak may be due to a reconstruction of the low-energy density of states due to interaction between soft harmonic oscillators. The interaction is enhanced with the frequency ω and, as a result, soft harmonic vibrations, localized for comparatively small ω, become extended (but not propagated) for bigger values of ω.

The local structure of ${\mathrm{As}}_{\mathit{x}}$${\mathrm{Te}}_{100\mathrm{-}\mathit{x}}$ glassy semiconductors has been studied using x-ray anomalous scattering and x-ray-absorption spectroscopy as a function of the composition. Two important findings are (a) tellurium (Te) atoms are twofold coordinated in arsenic (As) rich alloys (x>40), while the Te coordination suddenly increases to 2.4 at the stoichiometric ${\mathrm{As}}_{40}$${\mathrm{Te}}_{60}$ composition, which indicates a large fraction (about 50%) of threefold Te sites in this glass. This percentage of occupancy of the threefold Te sites remains almost constant with increasing further the Te concentration; (b) a significant level of chemical disorder, marked by the existence of homopolar As-As and Te-Te pairs in the first coordination shell, is observed for all the investigated glasses. At the ${\mathrm{As}}_{40}$${\mathrm{Te}}_{60}$ composition, nearly about the same amount of As-As and Te-Te pairs do exist in the first coordination shell. Thus the stoichiometric ${\mathrm{As}}_{40}$${\mathrm{Te}}_{60}$ composition is not a chemical threshold as it is the case for the Se- or S-based glasses. Based on these results, a number of peculiar and unique features in the physical properties of these glasses, such as the glass transition temperature (${\mathit{T}}_{\mathit{g}}$), the microhardness, the glass forming ability, and the electrical conductivity, can be understood.

The scaling properties of the energy spectra of a random-dimer system are studied to discern the nature of the states at and around the dimer energy (${\mathrm{\epsilon }}_0$). The system is described by a tight-binding Hamiltonian. The scaling behavior of bandwidths for ‖${\mathrm{\epsilon }}_0$‖<2 shows that the system contains extended states in the neighborhood of ${\mathrm{\epsilon }}_0$. This result is further substantiated by the scaling behavior of the total bandwidth. The number of nonscattered states is found to increase with the increase in chain length. The scaling behavior of bandwidths also shows that the width of the nonscattered states depends on the dimer energy and its concentration in the sample. These results are consistent with results obtained from the transmission coefficient analysis. When the dimer energy is at the band edge (${\mathrm{\epsilon }}_0$=±2), the bandwidth scaling analysis shows that states around ${\mathrm{\epsilon }}_0$ are algebraically localized. This result is further substantiated by the behavior of the site Green function. The significance of our results in understanding the anomalous electrical conductivity in polyaniline is discussed.

Polarized single-crystal Raman spectra of benitoite (${\mathrm{BaTiSi}}_3$${\mathrm{O}}_9$) were gathered and atomic displacements have been assigned to each line in the spectra from our interpretations of the Raman data, from determinations by Adams and Gardner in an earlier study, and from determinations by lattice-dynamics calculations. The spectra can be naturally divided into three frequency ranges, where lattice-dynamics calculations show that the 50 to 300 ${\mathrm{cm}}^{\mathrm{-}1}$ range contains Ba, Ti, ring translational, and ring rotational modes, the 300 to 800 ${\mathrm{cm}}^{\mathrm{-}1}$ range contains three-membered silicate ring breathing, stretching, and deformation modes, and the 800 to 1200 ${\mathrm{cm}}^{\mathrm{-}1}$ range contains Si-O bond-stretching modes. From our conclusions for benitoite, Raman features in the 300 to 800 ${\mathrm{cm}}^{\mathrm{-}1}$ range may be sensitive to changes in Si-O-Si bond angles, or to the number of silicate tetrahedra within planar rings.

This paper describes a theory for matter transport by the dumbbell mechanism in a random fcc alloy. By means of kinetic equations we have evaluated the phenomenological coefficients, ${\mathit{L}}_{\mathit{i}\mathit{j}}$, from the linear-response expressions. It is shown that all the exact expressions for ${\mathit{L}}_{\mathit{i}\mathit{j}}$ (i,j=A,B) can be obtained from this method in a random binary alloy dilute in component B when rotation and translation-plus-rotation jumps are allowed for all the dumbbells. The method can be extended to the more complex system of concentrated AB alloys.

Measurements of the Kapitza conductance ${\mathrm{\sigma }}_{\mathit{K}}$ made using a picosecond optical technique at temperatures between 50 and 300 K are presented for interfaces between metals and dielectrics. The Debye temperatures ${\mathit{FTHETA}}_{\mathit{D}}$ of the metals (Pb, Au, Al, and Ti) were in the range from 102 to 426 K, while those of the dielectrics (${\mathrm{BaF}}_2$, sapphire, and diamond) varied from 287 to 2200 K. Conductances measured between materials with ${\mathit{FTHETA}}_{\mathit{D}}$ differing by less than about a factor of 5 were found to be in reasonable agreement with calculations based on a lattice dynamical theory. However, for more widely mismatched solids the measured conductances were found to be greatly in excess of the lattice dynamical calculations. In some of these cases the conductances exceeded even the phonon radiation limit, indicating that much of the heat flow between the solids was via an inelastic channel. It was demonstrated experimentally that the inelastic channel does not involve an interaction between the phonons in the dielectric and electrons in the metal. We show that the anomalously large conductance can be understood in terms of a model in which the anharmonicity of the metal plays an important role.

The interaction between phonons and a two-dimensional (2D) electron gas is studied beyond the Migdal approximation. The analysis of the vertex function leads to the relative correction of ‖ImΣ(${\mathrm{\epsilon }}_{\mathit{p}}$,ω)‖ which is of the order of λ(${\mathrm{\Omega }}_{\mathrm{ph}}$+aT)${\mathit{E}}_{\mathit{F}}^{\mathrm{-}1}$ln(${\mathit{E}}_{\mathit{F}}$/${\mathrm{\Omega }}_{\mathrm{ph}}$). Here, ${\mathrm{\Omega }}_{\mathrm{ph}}$ is the average phonon frequency, and a(∼1) is the ratio between coupling constants for low-frequency and high-frequency phonon modes. For ‖ω‖≫${\mathrm{\Omega }}_{\mathrm{ph}}$ the correction is ‖ω‖/${\mathit{E}}_{\mathit{F}}$. The physically relevant result is that significant corrections are present only when ‖ω‖≲${\mathrm{\Omega }}_{\mathrm{ph}}$,‖ω-${\mathrm{\epsilon }}_{\mathit{p}}$‖≲${\mathrm{\Omega }}_{\mathrm{ph}}$ and they increase with temperature as ${\mathit{T}}^{\mathrm{\delta }}$ with δ≤1 in the entire frequency region. Also, our results strongly suggest that the quasiparticle picture for a 2D electron gas in a 3D lattice has to be corrected by many-particle effects even at small ${\mathrm{\omega }}_{\mathit{D}}$/${\mathit{E}}_{\mathit{F}}$.

T. Fukuhara, I. Sakamoto, and H. Sato [J. Phys.: Condens. Matter 3, 8917 (1991)] reported valence fluctuations of Sm ions in ${\mathrm{SmRuSn}}_3$, which orders antiferromagnetically at 6 K. We have carried out x-ray, microprobe, heat-capacity, susceptibility, and resistivity measurements on a sample of nearly the same stoichiometry. There are two inequivalent Sm sites in ${\mathrm{SmRuSn}}_3$ and from the analysis of our data we conclude that Sm ions at one site are in the trivalent state and those at the second site are either divalent or weakly valence fluctuating.

The assignment of the absorption spectrum of ${\mathrm{Y}}_3$${\mathrm{Fe}}_5$${\mathrm{O}}_{12}$ (YIG) made by Scott et al. [Phys. Rev. B 10, 971 (1974)] is shown to be incorrect and a new one is made by diagonalizing the complete cubic crystal-field matrices for ${\mathit{d}}^5$ ions, involving spin-orbit interaction, given by Zhou et al. [Phys. Rev. B 44, 7499 (1991)]. The Racah parameters B and C, the crystal-field parameter Dq, and the spin-orbit coupling coefficient ζ are determined (in units of ${\mathrm{cm}}^{\mathrm{-}1}$) as B=783.3(530), C=2928(3220), Dq=1336(1300), ζ=395 for octahedral ${\mathrm{Fe}}^{3+}$, and B=606.1(705), C=2696(2730), Dq=-1117.3(560), ζ=335 for tetrahedral ${\mathrm{Fe}}^{3+}$, where the numerals in parentheses are the values adopted by Scott et al. Furthermore, the cubic zero-field splitting parameter a of ${\mathrm{Fe}}^{3+}$ in YIG is calculated to be ${\mathit{a}}_{\mathrm{oct}}$=156×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$ and ${\mathit{a}}_{\mathrm{tet}}$=58.6×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$. The value for ${\mathit{a}}_{\mathrm{oct}}$ differs from the value of 189×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^{\mathrm{-}1}$ found for ${\mathrm{Fe}}^{3+}$ in ${\mathrm{Y}}_3$${\mathrm{Ga}}_5$${\mathrm{O}}_{12}$:${\mathrm{Fe}}^{3+}$. These results support speculations made by Geschwind [Phys. Rev. 121, 363 (1961)].

Multiband Hubbard and Pariser-Parr-Pople calculations have been carried out on mixed donor-acceptor (DA) stacks with doubly degenerate acceptor orbitals and nondegenerate donor orbitals at two-thirds filling. Model exact results for 2, 3, and 4 DA units show that McConnell’s prediction of high-spin ground states in these systems is, in general, incorrect. The larger phase space available for the low-spin states leads to their kinetic stabilization in preference to high-spin states. However, for large electron-correlation strengths, the direct exchange dominates over the kinetic exchange resulting in a high-spin ground state.

Measurements of the magnetic force and magnetic torque acting upon single-crystal and polycrystal samples of the heavy-fermion superconductor ${\mathrm{UBe}}_{13}$ have been made at temperatures from 60 mK to 30.0 K and in magnetic fields to 23 T using a capacitive magnetometer. The magnetic susceptibility deduced from the magnetic force is in reasonably good agreement with measurements using conventional techniques. We find that a large, anomalous contribution to the magnetic torque (AMT) appears in fields above 3–5 T at low temperature and at temperatures below about 7–12 K in high fields. The AMT coexists with the superconducting state at low temperature. We propose that the AMT reflects the existence of a field-induced magnetic phase transition. The presence of such a phase transition is consistent with specific-heat, thermopower, magnetoresistance, and Hall-effect measurements.