Materials Literature
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The authors have used molecular dynamics simulation to study the central peak recently discovered by quasi-elastic neutron scattering on SrCl 2 in the fast ion conducting state. They find that the peak appears as a component of the simulated partial dynamical structure factors. They find, in agreement with experiment,…
Inelastic neutron scattering has been used to measure the phonon dispersion relation along (001), (110) and (111) directions of a single crystal of Na<sub>2</sub>S at 50K. A simple shell model has been successfully fitted to the data. Dynamic quantities such as density of states, Debye temperature, displacement-displa…
Phonons in the quasi-one-dimensional compounds ZrS 3 , ZrSe 3 , ZrTe 3 and HfSe 3 have been investigated by Raman spectroscopy. Most of the structures observed have been assigned to Raman active zone centre phonons. Although twelve such k=0 optical phonons are theoretically predicted, some of them are still missing; p…
A review is given of experimental and theoretical work in the last few years which yields information about states in the gap in non-crystalline semiconductors. The discussion is limited to hydrogenated amorphous silicon (a-Si-H) and to the chalcogenides including selenium. Among issues treated are: the evidence for a…
A technique for directly measuring the static structure factor for electrons with use of synchrotron radiation is described. Results for the conduction electrons in beryllium and the basal plane of graphite show a peak at $k\ensuremath{\cong}2{k}_{\mathrm{F}}$ as predicted, but the pair correlation function shows an a…
The force transmitted through the layers of smectic-$A$ and smectic-$B$ phases of butyloxy-benzylidene-octylanine (4O.8) have been measured at frequencies between 1 and 10 000 Hz, in the presence of an ac shear parallel to the layers. It is found that the smectic-$A$ behaves as a viscous fluid. The smectic-$B$ shows a…
Reported here are polarocaloric (electrocaloric) measurements of a ceramic specimen of lead zirconate modified with ${\mathrm{Ti}}^{4+}$ and ${\mathrm{Sn}}^{4+}$. Temperature changes as large as 2.0 \ifmmode^\circ\else\textdegree\fi{}K were recorded. The temperature change varies roughly as the square of the polarizat…
It is shown that the PdM 4,5 N 4,5 N 4,5 Auger spectra of AgPd alloys do not approach an atomic spectral profile as the Pd concentration is reduced. This is contrary to the behaviour of Pd and Ag Auger spectra observed from alloys of these metals with Al and Mg, and is also contrary to the predictions of a previously…
Tunneling measurements have been performed on Nb-doped and reduced superconducting SrTi${\mathrm{O}}_{3}$. Beyond a certain carrier concentration, when a second conduction band gets filled, a distinctive double-gap structure is observed in Nb-doped samples. Its sharpness and anomalous temperature dependence can be rel…
A method for determination of lattice parameters of small particles is used which is not an integrale one – in contrast to the commonly employed techniques – and which is utmost sensitive for very small changes in lattice parameters. Thus individual particles can be investigated as well as the variation of lattice par…
The ordering of the trivalent and pentavalent cations in the perovskites Pb(Sc1/2Nb1/2)O3 and Pb(Sc1/2Ta1/2)O3 can be varied by suitable heat treatments. The degree as well as the kind of order strongly affects the character of the FE → PE phase transition. A spatially homogeneous disorder leads to a diffuse phase tra…
Solid state, low temperature IR (25–7400 cm−1) and Raman (100–2600 cm−1) spectra were obtained for Np(BH4)4 and Np(BD4)4 from which most of the allowed fundamentals were assigned based on the Td molecular structure. Those assignments were used in a normal coordinate analysis to derive a simple force field using eight…
Pulsed nuclear quadrupole resonance (NQR) experiments have been performed on three forms of elemental arsenic: amorphous ($a$), rhombohedral ($\mathrm{rh}$), and orthorhombic ($or$). The temperature dependence of the spin-lattice relaxation time (${T}_{1}$) provides evidence for the existence of disorder (tunneling) m…
Dielectric constant and the initial permeability of Fe 3 O 4 have been measured from 4.2 K to room temperature. Magnetic and dielectric relaxations were observed in the temperature range of 30 to 60 K. These relaxations were considered to be caused by the transfer of electron between ferrous and ferric ions. The magne…
Crystalline ${\mathrm{As}}_{2}$${\mathrm{S}}_{3}$ (orpiment) is a layer-structure semiconductor whose optical properties, under ordinary conditions, are determined by its diperiodic layer symmetry. We have investigated the effect of hydrostatic pressure on the optical-absorption edge and the Raman scattering spectrum…
The incorporation of homovalent ions, e.g., I− in AgBr, leads to a substantial increase in ionic conductivity σ. The charge compensation concept does not explain the enhancement. AgBr+30 mol. % AgI exhibits σ∼7 Ω−1 cm−1 at 380 °C, which is ∼170% larger than that of α-AgI, the best known supersonic conductor, at its me…
The pressure dependence of the Raman peaks of CuGa${\mathrm{S}}_{2}$ and AgGa${\mathrm{S}}_{2}$ (chalcopyrite structure) has been studied up to 20 GPa in a gasketed diamond anvil cell. Nonlinear pressure dependence of several phonon frequencies have been noted, including a softening of the lowest ${\ensuremath{\Gamma}…
The effects of large amplitude shearing rates on 108 particle amorphous Lennard-Jones systems have been examined. A resolution of the structural and dynamical properties reveals that there is a tendency for shear to reorganize the liquid into layers to facilitate flow and hence reduce shear viscosity. The first steps…
A simple phenomenological model is presented for the calculation of intensity of Stokes scattered light due to vibrations of molecules adsorbed on a metallic grating or a rough metal surface. The surface roughness is assumed to be represented by a superposition of sinusoidal gratings of different periodicities, with e…
We discuss the nature of the lattice instability in a highly disordered quasi-one-dimensional conductor, where the electronic states near the Fermi energy are localized in space. The resulting lattice and charge-density distortions are random in space and are frozen. The mathematical and physical similarities of this…