Electrical conductivity and oxygen nonstoichiometry of SrCo0.25Fe0.75O3-δ

The oxygen stoichiometry and defect structure of SrCo0. 25Fe0.75O3-δ were studied by solid-electrolyte coulometry, thermogravimetry, and conductivity measurements at temperatures from 20 to 1000‡C and oxygen partial pressures from 1 to 105 Pa. The results were used to construct thep-T-x andp-T-a phase diagrams and identify the sequence of phase transformations in the Co-substituted strontium ferrate (low-temperature perovskite → brownmillerite → high-temperature perovskite). SrCo0.25Fe0.75O3-δ was shown to be p-type throughout thepo 2 and temperature ranges studied. Cooling in flowing oxygen or air was found to give rise to sharp changes in the resistivity of SrCo0. 25Fe0.75O3-δ.