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1993 (2)
1Author    E. A. Zhurova, V. E. Zavodnik, S. A. Ivanov, P. P. Syrnikov, V. G. TsirelsonRequires cookie*
 Title    Electron Density and Anharmonic Thermal Atomic Vibrations in Kj_ x Li x Ta0 3 (* = 0, 0.05, 0.15) Perovskites  
 Abstract    The results of accurate X-ray diffraction studies of KTa0 3 , K 0 95 Li 0 05 TaO 3 and K 0 85 Li 0 15 Ta0 3 crystals are presented. Anharmonicity of the thermal motion of the oxygen atoms and deformation electron density maps are discussed. 
  Reference    Z. Naturforsch. 48a, 25—28 (1993); received November 8 1991 
  Published    1993 
  Keywords    Anharmonic thermal vibrations, Electron density, Chemical bond 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0025.pdf 
 Identifier    ZNA-1993-48a-0025 
 Volume    48 
2Author    Ullrich PietschRequires cookie*
 Title    Static and Dynamical Valence-Charge-Density Properties of GaAs  
 Abstract    Owing to the close neighbourhood of Ga and As in Mendeleev's table, GaAs shows two funda-mental classes of X-ray structure amplitudes distinguished by their extremely different scattering power. They are differently sensitive to the valence electron density (VED) redistribution caused by the chemical bond and must be measured by different experimental methods. Using such data, both the VED and the difference electron densities (DED) are calculated here. Comparison with theoret-ical densities shows that the VED is characterized by covalent, ionic and metallic contributions. The DED constructed from GaAs and Ge data demonstrates the electronic response caused by a "protonic" charge transfer between both f.c.c. sublattices as well as the transition from a purely covalent to a mixed covalent-ionic bond. Especially the charge-density accumulation between nearest neighbours (bond charge (BC)) depends on the distance between the bonding atoms and changes under the influence of any lattice deformation. This phenomenon is described by a BC-trans-fer model. Its direct experimental proof is given by measuring the variation of the scattering power of weak reflections under the influence of an external electric field. This experiment demonstrates that the ionicity of the bond changes in addition to the BC variation. 
  Reference    Z. Naturforsch. 48a, 29—37 (1993); received December 5 1991 
  Published    1993 
  Keywords    Valence charge density, GaAs, Chemical bond, Bond charge transfer, Ionicity 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0029.pdf 
 Identifier    ZNA-1993-48a-0029 
 Volume    48