title: β-Nb9VO25.
abstract: The title compound, nona-niobium vanadium penta-cosa-oxide, was prepared by a solid-state reaction at 1198 K. It is isotypic with Nb9AsO25, Nb9PO25 and Ta9VO25. The structure consists of NbO6 octa-hedra (one with 4/m.. and two with m.. symmetry) and VO4 tetra-hedra (-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 NbO6 octa-hedra and chains of NbO6 octa-hedra and chains of VO4 tetra-hedra. The V site shows half-occupancy, hence one half of the VO4 tetra-hedra is unoccupied. The structural differences with α-Nb9VO25, VOSO4, SbOPO4 and NbOPO4 oxides are discussed.
authors.affiliation: Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 El Manar Tunis, Tunisia.
authors.forename: Rawia
authors.initials: R
authors.lastname: Nasri
authors.affiliation: Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 El Manar Tunis, Tunisia.
authors.forename: Saïda Fatma
authors.initials: SF
authors.lastname: Chérif
authors.affiliation: Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 El Manar Tunis, Tunisia.
authors.forename: Mohamed Faouzi
authors.initials: MF
authors.lastname: Zid
authors.affiliation: Laboratoire de Matériaux et Cristallochimie, Faculté des Sciences de Tunis, Université de Tunis El Manar, 2092 El Manar Tunis, Tunisia.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Driss