The Electrochemical Oxidation : a New Way for Preparing Highly Oxidized Ferrites

Abstract
The electrochemical oxidation is depicted as a novel and powerful route 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 especially perovskite-type ferrites such as SrMO₃ ( M = Fe or/and Co ) or Sr₂LaFe₃O_9-ε. The characterization of the samples shows that they remain well crystallized after the electrochemical treatment and bulky oxidized. The reaction can be described as an intercalation process of oxygen atoms into the host lattice of the starting material. For instance, the chemical analysis as well as Mössbauer spectroscopy data of SrFeO₃ or of Sr₂FeCoO₆ reveal iron cations to be exclusively tetravalent. On the other hand, Sr₂LaFe₃O_9-ε exhibits at decreasing temperature a disproportionation of the mixed valence of iron. Potentiostatic and galvanostatic experiments have shown that the amount of intercalated oxygen can be controlled and that the process is reversible. A mechanism involving the formation of O^- species that can diffuse inside the bulk of the material, is proposed.