CORRELATION BETWEEN THE REACTIVITY TOWARDS OXYGEN AND THE COERCITIVITY IN SUBMICRON VANADIUM FERRITE SPINELS

Nanometric powders of Fe2VO4 and Fe1.84V0.92Co0.23O4 have been synthet ised by ''climate douce'' process. The cations in the spinel structure can oxidize at low temperatures without any phase transformation lead ing to cation-deficient spinel with formula Fe2V4+delta and Fe1.84V0.9 2Co0.23O4+delta, where delta is the deviation from stoichiometry, due to a change of the anion-cation ratio, consecutive to formation of vac ancies. The oxidation, investigated by thermogravimetry, involves seve ral stages, each stage corresponding to the oxidation of one oxidizabl e cation, Fe2+, V2+, V3+ on B (octahedral) or A (tetrahedral) sites. c oercivity has also been studied, revealing that the coercive field inc reases with the rate of oxidation.