New cation-deficient vanadium-iron spinels with a high vacancy content

New cation-deficient vanadium-iron spinels V(8x/(8+delta))Fe((24-8x)/(8+del ta))square(3 delta/(8+delta))O(4) have been obtained by the oxidation at lo w temperature (<500 degrees C) of the corresponding nanosized stoichiometri c spinels VxFe3-xO4 (0 less than or equal to x less than or equal to 2). Th e oxidation state of the cations and their distribution over both octahedra l (B) and tetrahedral (A) sites were partially investigated by associating thermal analyses (differential scanning calorimetry (DSC) and differential thermogravimetric (DTG)), X-ray diffraction, and infrared and X-ray photoel ectron spectroscopy. The high number of vacancies results of the Fe2+ to Fe 3+ and V3+ to V5+ through V4+ ions oxidation. This one may reach 0.90 per u nit formula for x = 2. (C) 2000 Elsevier Science Ltd.