Materials Literature
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Polarized, depolarized, isotropic, difference, and reduced Raman spectra were obtained from vitreous silica, irreversibly compacted at 600 °C and 50 kbar, to ambient densities as high as 2.73 g cm−3. The 60 cm−1 ‘‘Boson’’ peak; and, the intense optic, Si–O–Si bending peak at 440 cm−1 including its low-frequency should…
The weak-localization phenomenon for two-dimensional (2D) electronic systems is invoked to explain the negative magnetoresistance as well as the low-temperature dependence of the resistivity of pyrocarbon samples heat treated between 2000 and 2600 \ifmmode^\circ\else\textdegree\fi{}C. The 2D character is found to orig…
Optical absorption over a large dynamic range obtained by two different experimental techniques is reported for an undoped α-Al2 O3 single crystal. Absorption data are presented in two energy ranges: 0.94–3.5 eV and 4.5–8.6 eV. Vacuum ultraviolet (vuv) absorption measurements were performed on three boules of Czochral…
This work studies the pressure-induced semiconductor-to-metal transition (SMT) in the TmSe-TmTe alloy system. This SMT is accompanied by a valence instability of the Tm ions. Single-crystalline semiconducting ${\mathrm{TmSe}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Te}}_{\mathit{x}}$ alloys are investigated und…
We have used a new, approximate method for computing total energies and forces in covalent systems and investigated the electronic and vibrational spectra and equilibrium structures of small Si clusters (${\mathrm{Si}}_{\mathit{n}}$ with n=2--7). The method uses an electronic-structure tight-binding formalism based on…
Using a phenomenological lattice-dynamical theory in the quasiharmonic approximation, we present a comprehensive study to understand the effects of pressure on the vibrational properties of Ga-In pnictides that exhibit a sphalerite crystal structure. The existing pressure-induced Raman scattering data for phonon frequ…
First-order Raman scattering from graphite irradiated by an electron beam has been studied by using the laser microprobe technique. An approximately linear relation is exhibited between the linewidth of the ${\mathit{E}}_{2\mathit{g}}$ mode and the reciprocal of the crystallite size. The observed linewidths are larger…
Self-consistent ab initio band-structure calculations using the augmented-spherical-wave method were performed for the hypothetical compounds ${\mathrm{YFe}}_{12}$ and ${\mathrm{YFe}}_{8}$${\mathit{M}}_{4}$ (M=Ti, V, Cr, Mn, Mo, and W) with the ${\mathrm{ThMn}}_{12}$ structure, in which the M atoms occupy the 8(i) cry…
An interaction potential consisting of two-body and three-body covalent interactions is proposed for ${\mathrm{SiO}}_{2}$. The interaction potential is used in molecular-dynamics studies of structural and dynamical correlations of crystalline, molten, and vitreous states under various conditions of densities and tempe…
Molecular modeling of alcohol dehydrogenase suggests that His-47 in the yeast enzyme (His-44 in the protein sequence, corresponding to Arg-47 in the horse liver enzyme) binds the pyrophosphate of the NAD coenzyme. His-47 in the Saccharomyces cerevisiae isoenzyme I was substituted with an arginine by a directed mutatio…
Structural features of TiS2 were studied by scanning tunneling microscopy (STM) and single-crystal x-ray diffraction was applied as a complementary technique. STM images in air and at room temperature revealed, besides the trigonal symmetry of the lattice, several new features having this symmetry as well. We conclude…
The total decay rate of the 6 I 7/2 term level of Gd 3+ in YOCl and LiYF 4 is studied as a function of temperature. This rate is described as a termal average of the difference contributions of the crystal field components. The difference between the rates in YOCl and LiYF 4 is discussed.
In disordered superconducting Cu-Zr alloys with dilute magnetic impurities, we have observed a new type of resistance anomaly which gives rise to strongly increased scattering of conduction electrons in a narrow temperature range above ${\mathit{T}}_{\mathit{c}}$ and appears to be due to interaction between supercondu…
The phonon free energy is calculated for several silicon carbide polytypes using a valence overlap shell model. The three most commonly observed polytypes, i.e. (2), (23) and (3), are shown to be thermodynamically stable, with (2) and (3) as the low- and high-temperature phases, respectively, and (23) in between. The…
The relaxed structures of the (1), (2), (23) and (3) polytypes of silicon carbide are calculated using the pseudopotential total-energy technique with norm-conserving pseudopotentials and the local density approximation to the exchange-correlation energy. A 'tension model' is proposed to account for the atomic forces…
Using neutron-spin-echo and time-of-flight spectroscopy we have investigated the precise temperature dependence of the elastic (nonergodic) fraction in the spectrum of density fluctuations of the glass-forming polymer polybutadiene. With increasing temperature we found a critical decrease of the normalized elastic int…
Visible photoluminescence was observed in ultrafine Si particles at room temperature. Transmission electron microscopy revealed that Si microcrystallites were embedded in a Si oxide matrix for the sample which emitted the light. The emission energy depended on crystallite size in the range from 2.8 to 5 nm. The invers…
Abstract Various clay stabilizers are discussed, and methods are proposed for evaluating their effectiveness. Laboratory tests are used to rate the relative efficiency of potassium chloride vs other salts and organic compounds. Advantages and limitations of the various clay stabilizers are described. These studies sho…
Abstract The high strain rate response of polycarbonate (PC) and polymethyl methacrylate (PMMA) are measured using a split Hopkinson torsion bar for shear strain rates Ẏ from 500 s-1 to 2200 s-1, and temperatures in the range —100°C to 200°C. The yield and fracture behaviours are compared with previous data and existi…
The authors study finite-size corrections to the free energy in a two-dimensional random tiling model. This model is equivalent to an asymmetric six-vertex model and exhibits commensurate-incommensurate phase transitions of the Pokrovsky-Talapov type. They calculate finite-size scaling amplitudes of the free energy in…