Materials Literature
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The temperature dependence of the second-order Raman spectrum of SrTiO3 and KTaO3 has been observed over the temperature range 4°—473°K using the mercury 4358-Å exciting line. From group-theoretical arguments for cubic perovskite lattices the spectra have been interpreted in terms of phonon pairs at critical points in…
The electron spin resonance of F 3+ in single crystals of SrTiO 3 has been studied in the low temperature phase below 110°K. The resonance lines exhibited small splitting in addition to the usual tetragonal splitting. The orientation dependence of the splitting was measured at 77°K and at 4.2°K. The whole spectrum is…
Abstract A series of new aromatic polyethers have been prepared by solution condensation polymerization. The synthesis involves the condensation of a dialkali metal salt of a dihydric phenol with an “activated” or negatively substituted aromatic dihalide in an anhydrous dipolar aprotic solvent at elevated temperatures…
Abstract The frequencies of normal modes propagating in the high symmetry directions, [001], [110] and [111], of lead sulphide have been measured by inelastic neutron scattering techniques. A marked decrease in the value of the longitudinal optic mode frequency has been observed at small wavevectors. A similar effect…
In the morphogenesis of embryonic feather germs the formation of dermal cell groupings is associated with the development of a highly regular pattern of birefringence in the dermis. This birefringence is due to a lattice-like system of collagenous tracts along which dermal cells become progressively aligned and groupe…
The cross section for production of electron pairs by unpolarized photons in the field of an electron is calculated. The total cross section is obtained by numerical integration. The contributions to the total cross section from different diagrams (exchange and $\ensuremath{\gamma}\ensuremath{-}e$ terms) are calculate…
Compared to homologous tissues from adult animals, rapidly growing embryonic and fetal tissues contain large amounts of collagen proline hydroxylase. Lung and skin from scorbutic guinea pigs contain one-third as much enzyme as normal tissues do. A rapid increase in proline hydroxylase occurs on the 2nd day of formatio…
The self-consistent charge distribution in covalently bonded crystals and molecules is divided into two components, an atomic and a bonding part. Both can be calculated in elemental crystals from macroscopic dielectric properties. The theory is easily generalized to treat heteropolar and anisotropic effects, lattice v…
Numerous grains of gibbsite surrounded by zones of chlorite were found in six samples of sediment taken from Waimea Bay off the coast of Kauai, Hawaii. The chlorite has formed from the gibbsite, and growth bands in the chlorite either are parallel to chlorite-gibbsite interfaces or are concentric around small remnants…
Mössbauer spectroscopy has been used to investigate the early stages of phase separation in the Cu–Ni.7Fe.3 pseudobinary system. Our results indicate that new phase of composition close to the equilibrium composition is formed early in the decomposition, and grows in amount during transformation. The type of compositi…
The Seebeck coefficient, α, of semiconducting glasses based on vanadium pentoxide can be calculated from a knowledge of the concentration ratio of the high and low valence ions. The concentration of vanadium ions in the glass and long-range order apparently have no effect on α. Semiconducting glasses based on iron oxi…
Reflectance measurements for Ge films evaporated in situ are reported for 16 wavelengths between 490 and 1610 \AA{}, corresponding to photon energies of 25.2 and 7.7 eV. Measurements were taken after 3-min exposures to ambient pressures of 5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ Torr. Reflectance v…
The crystal structure of 16(CH3)3CNH2·156H2O has been determined from three-dimensional x-ray-diffraction data obtained at −30°C. The crystals are cubic, space group I4̄3d, with cell dimensions a=18.81±0.02 Å. The host framework of hydrogen-bonded water molecules consists of face-sharing heptakaidecahedra which have t…
Results of numerical calculations of energy transport in one- and two-dimensional lattice models are reported. Nearest-neighbor harmonic or anharmonic forces were used in randomly disordered mixtures of two different atomic masses. Opposite ends of the lattices were in contact with thermal reservoirs, which transfer e…
The role of the electronic properties of a semiconductor in heterogeneous catalysis and electrochemistry was experimentally investigated on single-crystal ZnO. It was shown quantitatively that the availability of electrons and holes at the surface is dominant in the mechanism of a heterogeneously catalyzed reaction. C…
A vibrational and attendant conformational analysis of the liquid n-paraffins and molten polyethylene is presented. For the purposes of the analysis a valence force field was derived which is applicable to both planar and nonplanar chains. The force field was evaluated from observed frequencies of trans (T) and gauche…
The Raman spectrum of crystalline quartz has been studied at temperatures between -196 and 615\ifmmode^\circ\else\textdegree\fi{}C. A weak mode of symmetry ${A}_{1}$ with room-temperature Raman shift of 147 ${\mathrm{cm}}^{\ensuremath{-}1}$ is found to grow in intensity and move towards zero Raman shift as the alpha-b…
The structure of Ca${\mathrm{Fe}}_{2}$${\mathrm{O}}_{4}$ has orthorhombic symmetry (space group ${{D}_{2h}}^{16}\ensuremath{-}Pnam$) and is characterized by Fe-O-Fe-O chains within which the Fe-O-Fe bond angle is \ensuremath{\sim}130\ifmmode^\circ\else\textdegree\fi{}. These chains are cross-linked by means of Fe-O-Fe…
The first appreciable decrease in the lifetime of the $^{2}E$ state of ${\mathrm{Cr}}^{3+}$ in ruby and emerald as the temperature is raised is shown to be the result of populating the shorter-lived $^{4}T_{2}$ level in thermal equilibrium with the metastable $^{2}E$. The direct transition from the $^{4}T_{2}$ to the…
The intensity of triplet-exciton annihilation luminescence in anthracene crystals at room temperature increases in weak magnetic fields up to a maximum increase of 5% at 350 Oe. For stronger fields the intensity decreases, finally leveling off at 80% of the zero-field value for $H\ensuremath{\gtrsim}5$ kOe. Sharp dips…