Disparity in electrical and magnetic properties of isostructural oxygen-deficient perovskites BaSrCo₂O_6−δ and BaSrCoFeO_6−δ

Despite having the same crystal structure, the two oxygen-deficient perovskites, BaSrCo₂O_6−δ and BaSrCoFeO_6−δ have significantly different electrical conductivity and magnetic properties, highlighting the important effect of oxygen stoichiometry. These two materials have been investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, variable-temperature electrical conductivity and magnetization studies. BaSrCo₂O_6−δ shows magnetic properties consistent with antiferromagnetic order, whereas BaSrCoFeO_6−δ exhibits the presence of uncompensated moments and short-range ferrimagnetism. XPS and iodometric titrations show a greater degree of oxygen vacancies in BaSrCo₂O_6−δ compared to BaSrCoFeO_6−δ. Cobalt is in di- and trivalent states in both compounds and iron is in tri- and tetravalent states in BaSrCoFeO_6−δ. The differences in electrical conductivity are remarkable, where BaSrCo₂O_6−δ shows nearly temperature-independent conductivity up to 400 °C, above which a semiconducting behavior sets in and persists up to 900 °C. However, BaSrCoFeO_6−δ exhibits semiconductivity up to 200 °C, followed by a downturn in conductivity from 200 to 900 °C, similar to the behavior observed in metallic systems.