Materials Literature
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The internal friction and dynamic modulus of W single crystals were measured after neutron irradiation near liquid-helium temperature. The results on dislocation pinning and the associated relaxation peaks suggest that in W the $〈110〉$ split interstitials perform a free migration at \ensuremath{\sim} 15 K (substage ${…
Abstract The infrared and photoelectron spectra of some substituted acetylacetones have been measured, and interpreted in terms of enolic and ketonic structures. Ionization potentials from specific orbitals have been assigned. With different substituents, the proportion of the two forms varies considerably. From measu…
X-ray photoemission spectra of W core levels in metallic sodium tungsten bronzes, ${\mathrm{Na}}_{x}\mathrm{W}{\mathrm{O}}_{3}$, clearly show asymmetries due to many-body effects. Na and O core levels show only the expected plasmon satellite, demonstrating the importance of the local density of states in the screening…
Neutron-scattering studies of $2H$-Nb${\mathrm{Se}}_{2}$ and $2H$-Ta${\mathrm{Se}}_{2}$ reveal the strong Kohn anomalies and incommensurate superlattice characteristic of charge-density-wave instabilities. Whereas the Nb${\mathrm{Se}}_{2}$ superlattice (${T}_{0}=33.5$ K) remains incommensurate to 5 K, Ta${\mathrm{Se}}…
Normal modes of vibration in vitreous SiO 2 , GeO 2 and BeF 2 are discussed from the point of view of the relative phase of motion of neighbouring atoms in the system. The notion of a phase quotient is introduced, as a criterion for determining the extent to which modes are acoustic or optical in character. Use of the…
The elastic properties of the four scheelite structure crystals CaMoO 4 , SrMoO 4 , PbMoO 4 and CaWO 4 are compared. Attention is given to the orientation dependence of the elastic behaviour and to how this is related to the atomic arrangement. With respect to the conventional definition of the XYZ axial set employed…
The lineshape of the A band in KBr:In+ and KCl:In+ has been measured as a function of temperature from about 16K to room temperature. The shape of the A band is well accounted for at low temperatures by a model that allows for spin-orbit coupling, vibrational coupling of the mod A), mod B) and mod C) states, and the d…
The atom positions in antiferromagnetic and ferroelectric BiFeO 3 have been obtained by profile analysis of powder neutron diffraction data collected ant 4.2K and 293K. The sublattice magnetization also determined at 4.2K, has been used to obtain a covalency parameter sum, A sigma 2 +2A pi 2 +A s 2 =13.4+or-0.5%. An e…
Sm–Co alloys close to the composition SmCo5 were investigated by metallographic, thermomagnetic, and X-ray diffraction methods. The effect due to evaporation losses of Sm on the equilibrium state of the Sm–Co alloys was studied. The results obtained do not support the suggestion of many workers for a unique stability…
A method for measuring and interpreting the Seebeck coefficient in high resistivity (≧ 105 Ωcm) materials is discussed; the technique is applied to pure V2O3 between 50 and 300 K. The results indicate that the low temperature phase of V2O3 is a band-type semiconductor.
The elastic moduli of a number of semiconducting phosphate glasses have been measured by ultrasonic techniques at 12 MHz. The dependence of elastic stiffness on glass composition is given for glasses of the MoO3–P2O5 and V2O5–P2O5 systems. The Debye temperatures of the phosphate glasses are in the range 300 to 450 K.
A model is developed for the green-yellow emitting centre in PbMoO4 and PbWO4 in terms of an excited state which can be visualized as Pb3+-XO3−4, i.e. an electron localized at XO and an electron-hole at one of the surrounding Pb2+ ions. The different levels of the triplet excited state arise from splitting due to the…
Ultraviolet spectroscopy confirms the findings of solubility studies that Sb(III) in 3–12 M hydrochloric acid solutions is present as an equilibrium mixture of SbCl 4 − and SbCl 6 3− ions. In the presence of H 2 SO 4 a further equilibrium with the SbCl 3 (HSO 4 ) − ion is found. The spectrum of the SbCl 6 3− ion in so…
The helicity amplitudes for electron-electron scattering to order ${e}^{4}$ are calculated by using the five invariant amplitudes presented in a previous paper. As applications, we rederive the unpolarized cross section given by Polovin and the spin-momentum correlation result obtained by Barut and Fronsdal.
Chloro−(tetraphenylporphinato)chromium(III) shows relatively normal visible (Q) bands in the region 610−500 nm and a relatively normal Soret (B) band at 447 nm; in addition, there are prominent bands in the near uv region 400−300 nm (2×104 < ε < 3×104 M−1⋅cm−1) and clear near ir bands in the region 820−6…
Exact calculations of heat flows and thermal conductivities in disordered harmonic chains of up to 50 atoms have been made within the framework of the self-consistent reservoir model. Thermal conductivities, obeying Fourier's law, are given as functions of the coupling to the internal heat baths for both fixed-end and…
A linear combination of localized orbitals-molecular orbital (LCLO-MO) cluster method is applied to calculate the electronic structure of ${{E}_{1}}^{\ensuremath{'}}$ centers in the $\ensuremath{\alpha}$-quartz structure of Si${\mathrm{O}}_{2}$. An ${\mathrm{O}}^{\ensuremath{-}}$ vacancy model, implying a net charge o…
Phase relationships in the copper/selenium system in the composition range 30–70 atomic % selenium have been studied at temperatures from 298 to 850 K and at pressures to 50 kbar. A revised atmospheric pressure phase diagram is given, as well as an outline of the phase diagram at 20 kbar.αCu 2 Se is monoclinic at 298…
Substitutional and displaced carbon impurities and an isolated nitrogen vacancy in hexagonal boron nitride are theoretically investigated by the "small periodic cluster" approach. The perfect-solid band structure is calculated from the solution of the eigenvalues of a finite and periodic cluster of atoms arranged acco…
Calculations of the vibrational density of states and the Raman and infrared spectra have been performed for random-network, microcrystalline, and polymorph structures of Si and Ge. The polymorphs considered include Si III, Ge III, and two clathrate structures. The calculations are based on simple semiempirical forms…