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Molecular orbital interpretation of x-ray emission and esca spectral shifts in silicates
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ABSTRACTS OF ARTICLES TO APPEAR IN
All of the nonmetallic solids that are known to possess high thermal conductivity have either the diamond-like, boron carbide, or graphite crystal structure. There are twelve different diamond-like crystals, a few boron carbide-type crystals, and two graphite structure crystals that have high thermal conductivity. Analyses of the rock-salt, fluorite, quartz, corundum and other structures show no candidates for this class. The four rules for finding crystals with high thermal conductivity are that the crystal should have (It) low atomic mass, (2) strong bonding, (3) simple crystal structure, and (4) low anharmonicity. The prime example of such a solid is diamond, which has the highest known thermal conductivity at 300 K. Received 13 January 1972 Revised 30 May 1972 10.
MOLECULAR ORBIT\L INTERPREThTION OF X-RAY EMISSION AND ESCA SPECTRAL SHIFTS IN SILICATES J.A. Tossell, Dept. of E. arid P. Science, 54—819, M.I.T., Cambridge, Mass. 02139.
J.
PHYS. CHEM. SOLIDS
Vol. 11. No. 7
Abstract-Rare earth chromium sulfides R CrS 3 ; R = Y, Gd, Dv, Ho arid Er have been synthesized by high temperature reaction of the respective oxides, R Cr03, with CS,. Single crystals have been grown by mineralization of the polycrystalline powders using halogen as a mineralizer. The crystal structures were determined from X-ray rotation and Weissenberg photographs. RCrS3, with R = Y, Gd, Ho and Er, were found to have an isostructural morioclinic structure, while DyCrS3 was found to have an orthorhombic structure, closely related to the monoclinic compounds. The optical absorption of these compounds, was well as of LaCrS3 whose structure was previously reported. was measured over the photon energy range 0.15 ~ 1.7eV. For all the compounds, a sharp absorption edge was found at 1.20 1.30eV at room temperature. This absorption edge shifts towards higher energy upon cooling from room temperature. The i.r. absorption of CrS3, HoCrS3 and ErCrS3 was negligible, while that of YCrS3, LaCrS3 and GdCrS3 increased markedly, with decreasing photon energy. Received 8 March 1972
An approximate molecular orbital theory is presented, tested, and applied to silicon and aluminium oxyanions.and The orbitalto structure of 4is calculated is used assign the Si0~ emission spectra. Calculations are performed X-ray at several internuclear distances and semiquantitative agreement is found with experimentally observed trends in ~lKct and SiK/3 spectra. Calculations on Si 7 yield fair 2O~ and A1SiO agreement with experimental trends relating to degrees of Si0 4 polymerization and to Al/Si ratio. Charges for bridging and non-bridging oxygens in Si20~, combined with point charge potentials from metal ions in the orthopyroxene structure yield Ols binding energies in agreement with ESCA results. Received 27 .4pril 1972 11.
CRYSTALLOGRAPHIC AND OPTICAL PROPERTIES OF RARE EARTH CHROMIUM SULFIDE S R CrS3 T. Takahashi, S. Osaka and 0. Yamada, RCA Research Laboratories, P.O. Box 5151, Tokyo InternationalInc., 100—31, Japan.
12.
ON HOLE AND IN ELECTRON SCATTERING EFFECTS ENERGY BAND INVESTIGATIONS BY PHOTONENHANCED FIELD EMISSION F.F. Körmendi, Institute for Chemical, Technological and Metallurgical Investigations, Beograd, Yugoslavia.
The detection of change in photo-modulated field-emission currents enables one to define not only the levels from which the excited electrons are ejected, but also on which levels the holes are created. The hole recombination processes determine the necessary absorbed light intensity in order to get measurable reduction in that part of field emission current which is due to electrons with energies between E~ and F, ± AE below the Fermi level. The analysis gives an estimate of the order of the parameters involved as a function of hole scattering type, band characteristics, etc. light It is intensities shown that are 2 absorbed i0~—10~ ~V/cm
ABSTRACTS OF ARTICLES TO APPEAR IN
All of the nonmetallic solids that are known to possess high thermal conductivity have either the diamond-like, boron carbide, or graphite crystal structure. There are twelve different diamond-like crystals, a few boron carbide-type crystals, and two graphite structure crystals that have high thermal conductivity. Analyses of the rock-salt, fluorite, quartz, corundum and other structures show no candidates for this class. The four rules for finding crystals with high thermal conductivity are that the crystal should have (It) low atomic mass, (2) strong bonding, (3) simple crystal structure, and (4) low anharmonicity. The prime example of such a solid is diamond, which has the highest known thermal conductivity at 300 K. Received 13 January 1972 Revised 30 May 1972 10.
MOLECULAR ORBIT\L INTERPREThTION OF X-RAY EMISSION AND ESCA SPECTRAL SHIFTS IN SILICATES J.A. Tossell, Dept. of E. arid P. Science, 54—819, M.I.T., Cambridge, Mass. 02139.
J.
PHYS. CHEM. SOLIDS
Vol. 11. No. 7
Abstract-Rare earth chromium sulfides R CrS 3 ; R = Y, Gd, Dv, Ho arid Er have been synthesized by high temperature reaction of the respective oxides, R Cr03, with CS,. Single crystals have been grown by mineralization of the polycrystalline powders using halogen as a mineralizer. The crystal structures were determined from X-ray rotation and Weissenberg photographs. RCrS3, with R = Y, Gd, Ho and Er, were found to have an isostructural morioclinic structure, while DyCrS3 was found to have an orthorhombic structure, closely related to the monoclinic compounds. The optical absorption of these compounds, was well as of LaCrS3 whose structure was previously reported. was measured over the photon energy range 0.15 ~ 1.7eV. For all the compounds, a sharp absorption edge was found at 1.20 1.30eV at room temperature. This absorption edge shifts towards higher energy upon cooling from room temperature. The i.r. absorption of CrS3, HoCrS3 and ErCrS3 was negligible, while that of YCrS3, LaCrS3 and GdCrS3 increased markedly, with decreasing photon energy. Received 8 March 1972
An approximate molecular orbital theory is presented, tested, and applied to silicon and aluminium oxyanions.and The orbitalto structure of 4is calculated is used assign the Si0~ emission spectra. Calculations are performed X-ray at several internuclear distances and semiquantitative agreement is found with experimentally observed trends in ~lKct and SiK/3 spectra. Calculations on Si 7 yield fair 2O~ and A1SiO agreement with experimental trends relating to degrees of Si0 4 polymerization and to Al/Si ratio. Charges for bridging and non-bridging oxygens in Si20~, combined with point charge potentials from metal ions in the orthopyroxene structure yield Ols binding energies in agreement with ESCA results. Received 27 .4pril 1972 11.
CRYSTALLOGRAPHIC AND OPTICAL PROPERTIES OF RARE EARTH CHROMIUM SULFIDE S R CrS3 T. Takahashi, S. Osaka and 0. Yamada, RCA Research Laboratories, P.O. Box 5151, Tokyo InternationalInc., 100—31, Japan.
12.
ON HOLE AND IN ELECTRON SCATTERING EFFECTS ENERGY BAND INVESTIGATIONS BY PHOTONENHANCED FIELD EMISSION F.F. Körmendi, Institute for Chemical, Technological and Metallurgical Investigations, Beograd, Yugoslavia.
The detection of change in photo-modulated field-emission currents enables one to define not only the levels from which the excited electrons are ejected, but also on which levels the holes are created. The hole recombination processes determine the necessary absorbed light intensity in order to get measurable reduction in that part of field emission current which is due to electrons with energies between E~ and F, ± AE below the Fermi level. The analysis gives an estimate of the order of the parameters involved as a function of hole scattering type, band characteristics, etc. light It is intensities shown that are 2 absorbed i0~—10~ ~V/cm