NiV3O8 single crystal structure determination and comparison with polymorphic forms of ZnV3O8 and MgV3O8

A low temperature form of NiV3O8 compound was synthesized by solid state ch emistry and its structure determined by single crystal X-ray diffraction. N iV3O8 crystallizes in the orthorhombic system with space group Pbcm and cel l parameters a = 7.2340(6) Angstrom, b = 10.0520(4) Angstrom, c = 8.3930(8) Angstrom. The structure is built up with puckered [(Ni2+/V4+)(2)O-7](n) la yers connected by [V2O7] pyrogroups. Examination of the coordination polyhe dra dearly shows that this compound is a pure vanadyl vanadate without a ho mogeneity range contrary to previous observations. Comparison with other re lated MV3O8 compounds (M = Zn; Mg) shows that these structures are built up with the same layers but both the way of pilling as well as the way of con nection via pyre group are different. These differences lead us to formulat e this structure as delta NiV3O8 to distinguish it from the low alpha and h igh beta temperature form of other MV3O8 compounds. The magnetic behaviour shows two critical temperatures (2 and 27 K) where ferromagnetic phases app ear. (C) 2001 Elsevier Science Ltd. All rights reserved.