Synthesis and stability region of stoichiometric nanocrystalline vanadium-iron spinel powders

Vanadium-iron spinels with nanometric sizes have been synthesized by a soft chemistry route. This way of elaboration consists of a coprecipitation fol lowed by thermal treatments at low temperatures. The last thermal annealing is performed under a reducing atmosphere in order to obtain the exact oxyg en stoichiometry (four oxygen atoms for three metal atoms in AB(2)O(4)). Be cause of the low temperatures used, very low oxygen partial pressures (betw een 10(-20) and 10(-30) Pa) have to be applied. For this purpose, a reducin g setup has been used. It consists of H-2/N-2/H2O gas mixtures, creating a reducing atmosphere with low oxygen partial pressure. This atmosphere can b e applied to a sample in a thermobalance, so the mass variations are correl ated with the oxygen content (or oxygen stoichiometry) in the sample. Therm al annealing under low oxygen partial pressure allows one to obtain stoichi ometric spinels of Fe3-xVxO4 (0 less than or equal to x less than or equal to 2).