Oxidation states of the transition metal cations in the highly nonstoichiometric perovskite-type oxide Ba0.1Sr0.9Co0.8Fe0.2O3-delta

The oxidation states of Fe and Co in the complex perovskite-type oxide Ba0.1Sr0.9Co0.8Fe0.2O3-delta were determined by means of X-ray absorption near edge structure (XANES) spectroscopy. Measurements performed in situ for 783 <= T/K <= 918 and 50 <= pO(2)/Pa <= 2 x 10(4) reveal that the electrons generated by reduction are not equally distributed between the Fe and Co cations. A comparison with thermogravimetric measurements indicates a discrepancy in the amount of oxygen lost from the sample. This discrepancy is an indication that not only are the transition metal cations reduced but the oxygen anions are, too. A model explaining the observed behaviour is proposed.