Materials Literature
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The experimental results of Imbusch on energy transfer between single ions and pairs in 0.003%–1% Cr3+:Al2O3 are re-examined. It is shown that the energy transfer can only be plausibly explained on the basis of orbitally dependent exchange rather than the electric quadrupole–quadrupole interaction as has been postulat…
The scattering of phonons by point defects in high concentrations and by electrons has been studied in the cubic transition metal carbides. The specimens were single crystals containing up to 24% carbon-atom vacancies: $\mathrm{Ti}{\mathrm{C}}_{x}$, $\mathrm{Zr}{\mathrm{C}}_{x}$, and $\mathrm{Nb}{\mathrm{C}}_{x}$, wit…
The nonrelativistic augmented-plane-wave (APW) method has been applied to calculate the band structure of Re${\mathrm{O}}_{3}$. An important feature of this calculation is that it includes corrections to the usual "muffintin" approximation. Because of convergence difficulties, the APW calculation has been carried out…
Vibronic borrowing in closed-shell aromatics is investigated by means of the cyclic-polyene model with the π electrons treated according to simple Hückel theory and the σ electrons treated as outlined by Longuet-Higgins and Salem. The basis set for the vibronic wavefunctions consists of single-product Born–Oppenheimer…
Ferroelectric Ba(4+x)Na(2 − 2x)Nb10O30, with a Curie temperature of 833°K, has a tungsten bronze-type structure and crystallizes in the orthorhombic system, with subcell lattice constants a = 17.59182 ± 0.00001, b = 17.62560 ± 0.00005, and c = 3.994915 ± 0.000004 Å at 298°K. The space group is Cmm2, and there are two…
First-order Raman scattering from BeO, ZnO, ZnS, and CdS, all having the wurtzite structure (${C}_{6v}$), has been investigated. A discussion of the effects of the competition between the long-range electrostatic forces and the short-range forces due to anisotropy in the interatomic force constants on the vibrational…
The density of vapor-deposited "amorphous" Ge was determined from x-ray-diffraction absorption measurements and found to be the same as the density of crystalline Ge within \ifmmode\pm\else\textpm\fi{}5%.
The NMR spectra of H, Cl, Rb, or Cs nuclei in antiferromagnetic ${\mathrm{Rb}}_{2}$Mn${\mathrm{Cl}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O and ${\mathrm{Cs}}_{2}$Mn${\mathrm{Cl}}_{4}$\ifmmode\cdot\else\textperiodcentered\fi{}2${\mathrm{H}}_{2}$O were used to study magnetic ordering in these…
Calorimetric, dielectric, and electrocaloric measurements have been performed on single-crystal samples of K${\mathrm{H}}_{2}$P${\mathrm{O}}_{4}$ in the neighborhood of the ferroelectric phase transition, and show that the transition is of first order, with a discontinuous entropy change of $({{0.0456}_{\ensuremath{-}…
The finite-electron-lifetime expressions for the longitudinal and transverse dielectric functions of a free-electron gas obtained by Lindhard in the self-consistent-field approximation are examined. It is shown that these results are incorrect, and appropriate expressions are developed for the case where the system ca…
The chemical and magnetic structures of the ${\mathrm{Zn}}_{x}{\mathrm{Ni}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ system have been determined using neutron diffraction for $x=0, 0.25, 0.50, \mathrm{and} 0.75$. The data yield a cation distribution (${{\mathrm{Zn}}_{x}}^{2+}{{\mathrm{Fe}}_{1\ensuremath{-}…
A theory of the relationship between curvature strains and electric polarization in liquid crystals is developed in analogy to piezoelectric theory in ordinary crystals. The theory may explain some recently observed phenomena in nematic liquid crystals.
Abstract In the presence of excess air the kinetics of reaction between CaO and PbO to form calcium plumbate are governed by the diffusion process described by Jander's kinetic model. The energy of activation of the process, as calculated from the Arrhenius equation, is 50 kcal/mol. In an air and nitrogen atmosphere (…
The phase diagram of Li 2 SO 4 -K 2 SO 4 has been determined by differential thermal analysis. By making use of ail improved method, the sensitivity of the measurements has been increased and we have found a number of new transitions, especially in the lithium sulphate rich region. We have also detected a new transiti…
Abstract Under experimental conditions in which the interaction between triplet dye and oxygen is an initiating process (D–O mechanism), the photosensitized oxidation of leucofluorescein in the aqueous solution (reaction (1)) has been found to decrease in rate with the increasing oxygen concentration and that the magn…
Abstract The reactivity of scoured Acala 4‐42 cotton before and after treatment with alkaline and acid swelling agents has been assessed by a number of methods. It is shown that the reactivity depends more on the type of swelling, whether it is interfibrillar or intrafibrillar, than on the degree of swelling achieved.…
Aerospace technology has established the demand for thermally stable polymers which retain useful properties at high temperatures. The reliability of a re-entry shield is directly dependent on the performance of the polymers used as ablators. Polymeric ablation materials are sacrificial and are classified as subliming…
Abstract It was found that anthracene (I) was converted to 9,10-anthraquinone (III) and bianthrone (IV) by irradiation via anthracene peroxide (II). The reaction proceeded most effectively in carbon disulfide. Also IV was found to be oxidized to III by oxygen in singlet state.
Abstract As discussed in this paper, melt treatment prior to crystallization, apparently proceeds by the following stages: partial melting; an insensitive region; and at higher temperatures, deactivation of nucleation sites. The deactivation‐region onset temperature is quite dependent on the subsequent crystallization…
The scanning electron microscope can be used to produce, in a way that is not possible with optical techniques or with casts of pore space, a quasi three-dimensional representation of the pore structure of sandstone, making it possible to determine the pore structure of sandstone, making it possible to determine the n…