Phase composition, oxidation state and electrical conductivity of SrFe1.5−xCoxOy

Mixed ionic and electronic conducting oxides SrFe1.5−xCoxOy (x=0–0.6) were investigated. In the layered Sr4(Fe,Co)6O13−δ phase dominant region (x<0.375), the average valence of the transition metals (Fe,Co) determined by iodometric titration decreases monotonically with increasing cobalt content and varies slightly with temperature. In the multiphase region (x≥0.375), the valence changes significantly with temperature. The electrical conductivity increases with increasing cobalt content. Unusual changes in electrical conductivity were observed at ∼900 °C in the multiphase region, which may be associated with the conversion of the contained perovskite phase into the layered phase.