Materials Literature
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Sodium niobate, NaNbO3, has seven structures belonging to the perovskite family, comprising the aristotype 1 (with the ideal perovskite structure) and six hettotypes 1 (structures with lower symmetry). The differences between them can be systematized in terms of two factors, displacement of Nb from the octahedron cent…
X‐ray diffraction, electron diffraction, and Raman scattering measurements are presented for dehydrated amorphous ZrO 2 . Although the material lacks sufficient crystallinity to diffract X rays, electron diffraction patterns indicate a microcrystallinity with a grain size of 15 to 30 A. Raman spectra characteristic of…
During the Indian Ocean Expedition of R/V "Meteor" phytoplankton samples were taken with a multiple closing net ("multinet") at 103 stations. In this material the diatoms were investigated. In all 247 taxa could be identified which belong to 242 species and 5 varieties or formae of 80 genera. Of these 1 variety, 15 sp…
Phase transitions in the solid solution Sr χ(Na 0.5Bi 0.5)l-χTiO3 have been studied by dielectric, pyroelectric and D-E characteristic measurements. An intermediate antiferroelectric phase has been observed in the composition range of 0 ⩽ χ ⩽ 0.5 of this system. These compositions undergo a ferroelectric-antiferroelec…
Methanation, the hydrogenation of carbon oxides to methane. has been the subject of a large number of catalytic studies during the past 70 years. In the earliest work. that of Sabatier and Senderens [l]. nickel was found to be a very efficient catalyst. Nickel is still the material of choice in most investigations of…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfrared studies of apatites. I. Vibrational assignments for calcium, strontium, and barium hydroxyapatites utilizing isotopic substitutionB. O. FowlerCite this: Inorg. Chem. 1974, 13, 1, 194–207Publication Date (Print):January 1, 1974Publication History Published online1 Ma…
This paper reviews the experimental studies of displacive phase transitions in solids. Primary emphasis is upon inelastic light scattering and neutron scattering; related infrared reflectivity measurements, as well as x-ray and EPR analyses are also summarized. Several prototype structures are considered in detail: (1…
A necessary criterion for brittle fracture in crystals is established, in terms of the spontaneous emission of dislocations from an atomically sharp cleavage crack. We have calculated the stability of a sharp crack against emission of a blunting dislocation for a number of crystals and crystal types in two dimensions…
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A new optically active biphenyl compound has been synthetised. By incorporating this in certain biphenyl nematogens, a chemically/photochemically stable room-temperature cholesteric liquid crystal is produced. This is of positive dielectric anisotropy and gives the cholesteric-nematic electro-optical phase-change effe…
A 75-keV electron beam with a low angular divergence (8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ rad) combined with a Wien filter spectrometer is used to examine the dispersion of radiative surface plasmons in thin oxidized aluminum films. The measurements agree with theory, provided the effect of the…
Measurements of the conductivity of single-crystal TTF-TCNQ are reported for pressures 0-20 kbar and temperatures 20-273\ifmmode^\circ\else\textdegree\fi{}K. The metal-insulator transition temperature increases about 1\ifmmode^\circ\else\textdegree\fi{}K/kbar. The conductivity at 273\ifmmode^\circ\else\textdegree\fi{}…
A theory is developed to explain the magnetic domain contrast observed by scanning electron microscopy using the method reported recently [4, 5]. The theory is based on a model which assumes that the contrast is due to the Lorentz deflection of the incident electrons inside the specimen. Using this model, the dependen…
Reflectance measurements, in situ, on freshly deposited thin lead films are carried out in the far uv. Optical constants and other useful functions such as ${\ensuremath{\epsilon}}_{1}$, ${\ensuremath{\epsilon}}_{2}$, $\ensuremath{-}\mathrm{Im}({\ensuremath{\epsilon}}^{\ensuremath{-}1})$, $\ensuremath{-}\mathrm{Im}{(\…
The thermal conductivity of a number of samples of vitreous silica has been measured between 1.5 and 20 K and between 65 and 300 K. The specimens were obtained from a number of manufacturers and were all high-purity optical-quality material. Above 65 K, the thermal conductivities of all the specimens were found to be…
A previous model calculation of the kinetics of hole diffusion in thallium-activated alkali iodides led to predictions concerning the role of binary electron-hole diffusion in the energy transport associated with the scintillation process. In this paper we report the resuls of time-resolved emission and absorption mea…
An attempt is made to locate the energy levels associated with iron and aluminum in the band gap of SrTi${\mathrm{O}}_{3}$. A relative energy-level scheme for these impurities is derived from data in the literature, principally ESR and optical absorption. Measurements of thermally stimulated current, electrical conduc…
Neutron scattering and specific-heat studies of the crystal fields in the rare-earth monophosphides are reported. It is found that the fourth-order crystal-field parameters for the phosphides and for other rare-earth pnictides fall on a universal curve which is close to that predicted by an effective-point-charge mode…
The electronic band structures of the ferroelectric semiconductor SbSI, whose crystal structure is very complex compared with the crystals for which the band calculations have been made up to the present, have been calculated by the pseudopotential method in the para- and ferroelectric phases. It is shown that this ma…
A detailed phenomenological theory of the triplet luminescence from self-trapped excitons in halide crystals is developed. Energy levels and wave functions are obtained by constructing and diagonalizing a Hamiltonian matrix. Coupled rate equations for the decay of the three lowest triplet levels are solved for the gen…