Materials Literature
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The dielectric function of an inhomogeneous system consisting of small particles in a dielectric host material is investigated using a lattice gas model to describe the topological disorder among the particles. By applying the coherent potential approximation, an effective single-particle polarisability is found, whic…
The integrated intensities and full width at half maximum (FWHM) of the 80 cm -1 Raman bands (hard modes) of ferroelastic Pb 3 (PO 4 ) 2 and Pb 3 (P 0.77 As 0.23 O 4 ) 2 were investigated in both the ferro and 'intermediate' phases for different polarisations as functions of temperature. The observed behaviour of thes…
This Symposium on "The Effects of Hostile Environments on Plastics" is to honor a Plastics Pioneer, Raymond B. Seymour. The co-chairmen David Garner and G. A. Stahl as well as this speaker are former graduate students of Dr. Seymour.
Organic molecular crystals exhibit three-wave nonlinear mixing efficiencies one or two orders of magnitude above that of Lithium Niobate. Beyond the basic common molecular features of these crystals (conjugation and intra-molecular charge transfer), different possibilities to achieve a proper lattice orientation (chir…
Studies of the basic physics of nonlinear second order optical processes in solids remain critically important to the field of nonlinear optics and to further advances in telecommunications technologies. This fact receives continued emphasis today in problems of current interest such as phase conjugation and optical b…
Over the past decade it has been learned that organic materials containing appropriately constituted or substituted conjugation systems may exhibit highly enhanced electronic nonlinear optical polarization responses ( 1 - 4 ). Since the microscopic second-order nonlinear hyperpolarizability tensor, β, is orientational…
The electron paramagnetic resonance (EPR) and Mössbauer properties of native horseradish peroxidase have been compared with those of a synthetic derivative of the enzyme in which a mesohemin residue replaces the natural iron protoporphyrin IX heme prosthetic group. The oxyferryl pi cation radical intermediate, compoun…
The exchange interaction between ${^{3}\ensuremath{\Sigma}_{\mathrm{g}}}^{\ensuremath{-}}$ ${\mathrm{O}}_{2}$ molecules, as obtained from ab initio calculations for a singlet, triplet, and quintet dimer, can be well represented by the Heisenberg Hamiltonian. The coupling parameter $J$ depends exponentially on the ${\m…
A general class of models is introduced which relate the motion of a phase boundary to properties of the local interfacial geometry. These systems can undergo successive destabilizations as they grow, possibly giving rise to nonequilibrium spatial patterns. This formalism has applications to a wide variety of physical…
For pt.II see ibid., vol.16, p.2455 (1983). The temperature and pressure dependences of the elastic and strain-related properties of the 'pseudo-proper' ferroelectric material BiVO 4 have been determined using mean-field theory. In the tetragonal paraelastic phase the elastic constants c 11 -c 12 , c 66 and c 16 are a…
For pt.IV see ibid., vol.16, p.5119 (1983). Measurements of the Bi 3+ displacement and the primary and secondary spontaneous strains in the ferroelastic material BiVO 4 have been made as a function of temperature by single-crystal X-ray diffraction. The results are discussed using both macroscopic and microscopic mean…
For pt.V see ibid., vol.16, p.5127 (1983). The relationship between the domain wall orientation and the spontaneous strain in ferroelastics is discussed, with particular reference to the W' walls in BiVO 4 . The microscopic, wall-defining property is shown to be the coherence of the lattices of the twin components. Th…
The effect of doping of Tl upon thermoluminescence, its emission and optical absorption in flux grown BaFCl crystals is investigated. Besides an increase in luminescence output, X/γ-irradiations of BaFCl: Tl crystals produce three additional glow peaks at 450,465, and 500 K and a TL emission spectrum at 460 nm. Optica…
The grain cathodoluminescence (CL) properties of bariumtitannte ceramics, sintered at, different oxygen partial pressures are systematically investigated. The spectra are found to be composed of different bands, the intensities of which depends strongly on the specimen temperature and on the oxygen partial pressure of…
In the analysis of the thermoluminescence glow curves, and in particular when applied to TL dosimetry and TL dating of archaeological and geological samples, a first order behaviour of the peaks involved is usually implicitly assumed. In this work the TL response for second order kinetics is described and shown that t…
Studies of the structural phase transition of CsPbCl3, are carried out, using X-ray and neutron diffraction, NQR and Raman scattering below room temperature. It is confirmed that there is a second-order transition at about 200 K (TC4). From the structural analysis, it is determined that, at room temperature, the struc…
The intensities of photoluminescence lines D1 through D4 and also of the background component that are characteristic in a dislocated silicon crystal are measured as a function of the temperature. All of them become weaker as the temperature is raised. Such behaviour is interpreted in a quantitative way with the model…
We report the first observation of a pressure-induced phase transition in LiI${\mathrm{O}}_{3}$. A new phase appears when $\ensuremath{\beta}\ensuremath{-}\mathrm{Li}\mathrm{I}{\mathrm{O}}_{3}$ is compressed hydrostatically at room temperature, beyond 50 kbar. This is a reversible first-order transition with negligibl…
The thermal conductivity of an anharmonic crystal containing randomly distributed substitutional defects due to impurity-phonon scattering is theoretically investigated with the use of the method of double-time thermal Green's functions and the Kubo formalism considering all the terms, i.e., diagonal, nondiagonal, cub…
Polycrystalline ${\mathrm{H}}_{2}$S${\mathrm{O}}_{4}$ and ${\mathrm{H}}_{2}$Se${\mathrm{O}}_{4}$ were studied by powder neutron-diffraction techniques at temperatures near the melting points and at 10 K. This work was undertaken to determine hydrogen positions and to search for order-disorder transitions in the hydrog…