Electron densities in VN. I. High-precision x-ray-diffraction determination of the valence-electron density distribution and atomic displacement parameters

Journal Article · Wed Jul 15 00:00:00 EDT 1987 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.36.1415· OSTI ID:6229576

Kubel, F; Flack, H D; Yvon, K

High-precision, high-resolution x-ray-diffraction measurements were performed on a nearly stoichiometric, spherical single crystal of vanadium nitride (NaCl structure, a = 4.137 11(4) A) using Ag K..cap alpha.. radiation. Structure factors with an average accuracy of 0.05e were obtained for 90 unique reflections from 12 807 intensity profiles measured at room temperature. Effects due to anisotropic extinction and crystal inhomogeneity were modeled and refined together with a scale factor, metal-atom 4s and 3d and nonmetal-atom 2s and 2p orbital-occupancy factors, kappa expansion-contraction parameters, atomic site occupation, and anharmonic thermal parameters. At convergence, the reliability factors were R = 0.0068 (before) and R = 0.0031 (after) averaging symmetry-equivalent reflections. The charge distribution around the metal sites showed a positive deformation along (111), corresponding to preferential occupancy of t/sub 2//sub g/ orbitals. A comparison with isostructural TiC/sub 0.94/ and TiN/sub 0.99/ showed that the shape of the metal atoms as expressed by the orbital-occupancy ratio p(t/sub 2//sub g/)/p(e/sub g/) changes as a function of valence-electron concentration: p(t/sub 2//sub g/)/p(e/sub g/) = 3.3 in VN/sub 1.00/, 1.9 in TiN/sub 0.99/, and 1.0 in TiC/sub 0.94/, in agreement with theoretical predictions.

• Research Organization: Laboratoire de Cristallographie aux Rayons X, Universite de Geneve, 24 quai Ernest Ansermet, CH-1211 Geneve 4, Switzerl
• OSTI ID: 6229576
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Vol. 36:3
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
VANADIUM NITRIDES
ELECTRON DENSITY
STRUCTURE FACTORS
X-RAY DIFFRACTION
ELECTRON TRANSFER
LATTICE PARAMETERS
MEDIUM TEMPERATURE
MONOCRYSTALS
STOICHIOMETRY
SUPERCONDUCTIVITY
TRANSITION TEMPERATURE
COHERENT SCATTERING
CRYSTALS
DIFFRACTION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
NITRIDES
NITROGEN COMPOUNDS
PHYSICAL PROPERTIES
PNICTIDES
SCATTERING
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS
360204* - Ceramics
Cermets
& Refractories- Physical Properties