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1993 (4)
1Author    R. O. Horenian, W. WeyrichRequires cookie*
 Title    Momentum-Density Studies of Some Compounds with Triatomic Linear Anions  
 Abstract    High-purity powder samples of lithium and sodium azide (LiN 3 , NaN 3), cyanate (LiOCN, NaOCN) and hydrogen fluoride (LiFHF, NaFHF) were studied by means of 59.54 keV Compton spectroscopy. The measured isotropic Compton profiles were corrected for multiple scattering and transformed to spherically averaged reciprocal form factors B a (s). The experimental results are compared with theoretical reciprocal form factors obtained from Hartree-Fock calculations with different types of basis sets (Gaussian-and Slater-type orbitals, with and without polarisation functions) both for the free ions and for several kinds of clusters. The importance of intraionic and interionic interaction for the description of chemical bonding in these compounds is pointed out and discussed. 
  Reference    Z. Naturforsch. 48a, 325—333 (1993); received January 28 1993 
  Published    1993 
  Keywords    Compton spectroscopy, Azides, Hydrogen fluorides, Cyanates, Ionic crystals 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0325.pdf 
 Identifier    ZNA-1993-48a-0325 
 Volume    48 
2Author    V. A. Khokhlov, A. O. Kodintseva, E. S. FilatovRequires cookie*
 Title    "Anomalous" Thermal Conductivity of Crystalline Alkali Halides Close to Their Melting Point  
 Abstract    The thermal conductivity of crystalline alkali halides MX (M = Li, Na, K, Rb, and Cs; X = C1, Br, and I) close to their melting point has been measured by the steady-state coaxial-cylinders method. It was found to change anomalously as the temperature varied. A minimum of the thermal conduc-tivity at a characteristic temperature depends on the ionic composition of the crystal. This effect is ascribed to the formation of cooperating defects in the melting lattice. An expression relating the thermal conductivity of the ionic crystal near the melting point to the concentration of these defects is proposed. 
  Reference    Z. Naturforsch. 48a, 595—598 (1993); received April 25 1992 
  Published    1993 
  Keywords    Thermal conductivity, High temperature, Melting point, Ionic crystal, Alkali halide 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0595.pdf 
 Identifier    ZNA-1993-48a-0595 
 Volume    48 
3Author    NielsK. HansenRequires cookie*
 Title    Electrostatic Properties of Ions in Crystals from X-Ray Diffraction Data  
 Abstract    A procedure for calculating the electrostatic potential and the electrostatic energy of an ion in a crystal is presented. It is based on a mixed direct and reciprocal space approach, and it takes into account the detailed charge density distribution in the crystal which can be obtained from accurate X-ray diffraction measurements. 
  Reference    Z. Naturforsch. 48a, 81—84 (1993); received December 24 1991 
  Published    1993 
  Keywords    Electrostatic potential, X-ray diffraction, Charge density, Ionic crystals, Ionic con-duction 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0081.pdf 
 Identifier    ZNA-1993-48a-0081 
 Volume    48 
4Author    Tanja Asthalter, Wolf WeyrichRequires cookie*
 Title    The Anisotropy of the Reciprocal Form Factor and the Electronic Structure of Crystalline Lithium Hydride  
 Abstract    New high-precision measurements of the isotropic as well as of three directional Compton spectra of lithium hydride have been carried out using 24 'Am as a y-ray source. In order to account for the extreme sensitivity of LiH powder to atmospheric moisture, the final data (i.e. the reciprocal form factor) were corrected for the LiOH content determined by titrimetric analysis. For the interpreta-tion of the data, theoretical calculations were carried out using a Hartree-Fock program for periodic systems (CRYSTAL). Basis sets published by Dovesi et al. were used, one of which allows for polarisation of both the hydride and lithium ions. Comparison of the theoretical data with the experiment shows much better agreement of the results of complete solid-state calculations that take into account higher-order effects (polarisation and covalency) than those obtained by Löwdin orthogonalisation of free-ion wave functions (which assumes pure ionicity, neglecting all but first-order effects). The influence of further polarisation functions on the reciprocal form factor is inves-tigated and discussed. The remaining discrepancies are attributed to electron-electron correlation. 
  Reference    Z. Naturforsch. 48a, 303—309 (1993); received January 13 1993 
  Published    1993 
  Keywords    Compton spectroscopy, Reciprocal form factor, Ionic crystal, Electronic structure, Lithium hydride 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0303.pdf 
 Identifier    ZNA-1993-48a-0303 
 Volume    48