THE ELECTROCHEMICAL OXIDATION - A NEW WAY FOR PREPARING HIGHLY OXIDIZED FERRITES

The electrochemical oxidation is depicted as a novel and powerful rout e for preparing highly oxidized ferrites. The reaction is achieved at room temperature, in air, in alkaline solution (1M KOH or NaOH). This process has been used for preparing various new compounds and especial ly perovskite-type ferrites such as SrMO3 (M = Fe or/and Co) or Sr2LaF e3O9-epsilon. The characterization of the samples shows that they rema in well crystallized after the electrochemical treatment and bulky oxi dized. The reaction can be described as an intercalation process of ox ygen atoms into the host lattice of the starting material For instance , the chemical analysis as well as Mossbauer spectroscopy data of SrFe O3 or of Sr2FeCoO6 reveal iron cations to be exclusively tetravalent. On the other hand, Sr2LaFe3O9-epsilon, exhibits at decreasing temperat ure a disproportionation of the mixed valence of iron. Potentiostatic and galvanostatic experiments have shown that the amount of intercalat ed oxygen can be controlled and that the process is reversible. A mech anism involving the formation of O- species that can diffuse inside di e bulk of the material, is proposed.