Room Temperature Electrochemical Redox Reactions of the Defect Perovskite SrFeO_2.5+x

The electrochemical and chemical oxidation of the defect perovskite SrFeO 2.5 to the cubic perovskite SrFeO 3 at ambient temperature in alkaline electrolyte are shown to be in principle reversible processes with the appearance of intermediate compounds; the oxidation can be described by the formation of line phases SrFeO 2.75 and SrFeO 2.87 and one solid solution range SrFeO 3 - x with 0 ≤ x ≤ 0.03. The structure of the brownmillerite type parent phase is characterized by the presence of stacking faults in the octahedral and tetrahedral sequence of layers whose concentration increases significantly upon formation of the intermediate phases. Models based on observed microscopic features are discussed in order to explain the unusual phenomenon of room temperature oxygen transport.