Re-Investigation of the Structure of 7Bi2O3 · 2WO3 by Single-Crystal X-ray Diffraction

Abstract

The structure of the oxygen-deficient compound 7Bi2O3 · 2WO3, a fluorite-derivative phase considered a candidate for electronic applications because of its high ionic conductivity, is investigated by singlecrystal X-Ray diffraction employing Ag-Kα radiation (λ = 0.5608 Å) to minimize the effect of the absorption by the heavy metals. The space-group type is I41, the acentric subgroup of I41/a that was previously suggested from powder-diffraction data and precession-camera photographs. Lattice parameters are a = 12.513(2), c = 11.231(4) (Z = 2.5). The sample is twinned by syngonic merohedry, class I, with volume ratio of the individuals 0.58/0.42. The ordering of W partly confirms previous models, with one W fully occupying one of the sites on special position. However, the remaining W goes in a site on general position, which shares with Bi, resulting thus more diluted in the structure. The oxygen vacancies are partly ordered in three of the ten anion sites.