ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
X-ray diffraction intensities were measured from a BeO single crystal with wurtzite structure specially treated to reduce extinction effects. Preliminary least-squares refinement yielded experimental structure factors on an absolute scale, corrected for extinction and anomalous dispersion, and a reference model Be2+O2- with position parameter z = 0.3778 (4) and anisotropic Debye-Waller factors corresponding to atomic mean-square displacements with spherical average (u2) = 0.0045 (3) and 0.00353 (1) Å2 and prolateness (u23) - (u2) = 0.0008 (4) and 0.00005 (9) Å2 for Be2+ and O2-, respectively. The residual differences Fo- Fc (of these experimental structure factors and those of the reference model) were analysed in terms of site-symmetrized multipole expansions. The phases of Fo were refined iteratively to take into account the effect of the significant multipole components found. The contribution of the Be2+ ion was subtracted to make possible a study of the oxygen lattice. Significant multipole components of third, fourth and sixth order indicate that the oxygen in BeO forms bonded hexagonal O2- planes. They build up diffuse O-O bridges strongly bent towards the stabilizing Be2+ ions above the plane. The Be2+ ions exhibit a stretching quadrupole-like deformation suggesting some covalency of the bonding they build between the O2- planes. There is some evidence of anharmonicity of atomic vibrations, particularly in the direction of the hexagonal axis.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0108767387099057
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