Intermediate valencies of vanadium cations appearing during oxidation of vanadium–iron spinels

The oxidation state of vanadium cations in nanosized vanadium–iron spinels at stoichiometry and at oxidative nonstoichiometry has been investigated by associating X-ray diffraction, thermal analysis (DSC), infrared and X-ray photoelectron spectroscopies. It has been established that, during oxidation, the V3+ cations present several intermediate valencies before to realize the final oxidation state +5. A comparison was made with the oxidation of V2O3.