Phase relations in oxygen-deficient SrCoO2.5-δ

Several different methods have been applied in order to investigate phase relations in the oxygen-deficient perovskite SrCoO2.5-delta with respect to temperature and oxygen partial pressure. Three different polymorphs of strontium cobaltite have been detected: the rhombohedral phase (delta less than or equal to 0.16), the cubic pseudo-perovskite, probably existing in ordered microdomains (0.16 less than or equal to delta less than or equal to 0.21) and the disordered cubic perovskite (delta greater than or equal to 0.21). The standard thermodynamic functions (enthalpy and entropy) for the corresponding phase transitions have been calculated. The kinetics of transformation of cubic pseudo-perovskite --> rhombohedral phase have been studied in air at different temperatures. (C) 1999 Published by Elsevier Science B.V. All rights reserved.