β-Nb9VO25

Abstract

The title compound, nonaniobium vanadium pentacosaoxide, was prepared by a solid-state reaction at 1198 K. It is isotypic with Nb9AsO25, Nb9PO25and Ta9VO25. The structure consists of NbO6octahedra (one with 4/m.. and two withm.. symmetry) and VO4tetrahedra (-4.. symmetry) sharing corners and edges to form a three-dimensional framework. This framework can be considered as a junction between ribbons made up from NbO6octahedra and chains of NbO6octahedra and chains of VO4tetrahedra. The V site shows half-occupancy, hence one half of the VO4tetrahedra is unoccupied. The structural differences with α-Nb9VO25, VOSO4, SbOPO4and NbOPO4oxides are discussed.