Phase relation and oxygen‐non‐stoichiometry of Perovskite‐like Compound SrCoO x (2.29 < x > 2.80)

Strontium cobaltates in the composition range, SrCoO 2.29 ‐SrCoO 2.80 , have been prepared under various conditions with respect to the oxygen pressure and temperature. Samples prepared at high temperatures (above 800°C) crystallized in the brownmillerite or perovskite type Structure Depending on oxygen Deficiency. A perovskite phase having large oxygen Deficiency, SrCoO 2.29 , and a brownmillerite solid solution, SrCoO x (2.42 < x < 2.52), were observed. On the other hand, samples annealed at low temperatures (below 800°C) did not crystallize in 2H type Structure with Sr:Co ratio of 1:1 but in the cobalt Deficient phase, 2H‐SrCo 1‐u O x (u ≈ 0.1) and Co 3 O 4 . The high oxygen content perovskite SrCoO 2.67‐2.80 was obtained by annealing the brown‐millerite phase under high oxygen pressures at 300°C. The electrical conductivity of SrCoO x (2.29 < x < 2.80) and the oxygen diffusion coefficient of the perovskite phase SrCoO x (x = 2.68, 2.75 and 2.80) were measured as a function of temperature. SrCoO 2.80 showed the very high diffusion coefficient of 2.3 × 10 −11 cm 2 sec −1 at 23°C.