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

New cation-deficient vanadium–iron spinels V8x/(8+δ)Fe(24−8x)/(8+δ)□3δ/(8+δ)O4 have been obtained by the oxidation at low temperature (<500°C) of the corresponding nanosized stoichiometric spinels VxFe3−xO4 (0 ≤ x ≤ 2). The oxidation state of the cations and their distribution over both octahedral (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 photoelectron spectroscopy. The high number of vacancies results of the Fe2+ to Fe3+ and V3+ to V5+ through V4+ ions oxidation. This one may reach 0.90 per unit formula for x = 2.