The thermodynamics of oxygen intercalation in strontium ferrite SrFe_(2.5+δ) is studied by means of the coulometric titration technique. The analysis of the oxygen concentration dependent behavior of partial thermodynamic functions reveals inhomogeneous architecture of the ferrite, which can be viewed as consisting of microscopic brownmillerite-like domains intergrown with perovskite-like structural fragments. The oxygen vacancies are mainly located in the brownmillerite-like domains. The oxygen intercalation results in a gradual increase of the perovskite-like fragments and delocalization of the hole carriers. The changes in conductivity and thermopower with oxygen content can satisfactorily be explained in frameworks of a small-polaron conduction model.
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