The crystal structure of monoclinic wolfram vanadium oxide, W3V5O20, an OD structure related to R-Nb2O5
1970; Elsevier BV; Volume: 1; Issue: 3-4 Linguagem: Inglês
10.1016/0022-4596(70)90129-5
ISSN1095-726X
AutoresMats Israelsson, L. H. E. Kihlborg,
Tópico(s)Catalytic Processes in Materials Science
ResumoThe monoclinic ternary phase in the WVO system reported by Freundlich has been studied by X-ray diffraction methods. A careful phase analysis indicates a composition close to W3V5O20 and this is confirmed by the results of the crystal structure determination. The least-squares refinement of the structure resulted in a conventional R = 0.073. The unit cell dimensions are a = 24.41 Å, b = 7.446 Å, c = 3.950 Å, β = 91.03° and the space group is C2m. The structure is basicly the same as that of R-Nb2O5 and (Mo0.3V0.7)2O5 which are built up of MO6 octahedra sharing edges and corners as in V2O5 although with a different pattern for the off-center displacements of the metal atoms inside the octahedra. Wolfram and vanadium are partly orderly distributed which gives rise to a superstructure. Two positions are occupied by W and V, respectively, and the third statistically by (14 W + 34 V) with no indications of order. ESCA measurements and considerations of the MO bond lengths suggest that wolfram is hexavalent while vanadium is pentavalent in the singly occupied position and tetravalent in the site shared with wolfram. The structure is an OD structure, since a part of the diffraction spots is diffuse. A model is proposed which explains the partial disorder as due to mistakes analogous to stacking faults.
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