[摘要]：Ba(0.8)Sr(0.2)Co(0.8)Fe(0.2)O(3-delta) exists as a single cubic phase at 1000 degrees C in air. Upon slow cooling, it transforms, between 900 and 700 degrees C, to a mixture of cubic, hexagonal, and rhombohedral phases, as evidenced by X-ray diffraction and transmission electron microscopy. The reversible phase change is accompanied by a large change of the oxygen content (Delta delta = 0.14) of Ba(0.8)Sr(0.2)Co(0.8)Fe(0.2)O(3-delta) and a volume change of 1.2 vol% at 700-900 degrees C. The multiphase material shows lamellar shaped structures in the HRTEM micrographs due to the partial transformation of the material from the cubic to the hexagonal and rhombohedral symmetries. The electrical conductivity changes from p-type semiconductivity between room temperature and 700 degrees C to metal-like conductivity at higher temperatures up to 1000 degrees C. The electrical conductivity is irreversibly changed upon thermal cycling due to the formation of microcracks.
