Structural properties of vanadium oxides

It is shown that two vanadium oxides of unknown composition, i.e. VO_x [Tilley & Hyde, J. Phys. Chem. Solids, (1970), 31, 1613-1619] and phase Q [Colpaert, PhD Thesis, Rijksuniv. Gent (1972)] are identical with V₄O₉ [Théobald, Cabala & Bernard, C. R. Acad. Sci. Paris, SOr. C, (1969), 269, 1209-1212]. The unit cell of V₄O₉ is orthorhombic, with a = 8.235, b = 10.32, c = 16.47 Å. A model for the structure of V₄O₉ is proposed. It is based on an ordered superlattice of O vacancies in V₂O₅, and is in agreement with X-ray oscillation photographs. The model accounts for the low density of this material, its low temperature of formation, the typical appearance of twins and the topotaxic growth of V₄O₉ on V₂O₅.