Phase relations in oxygen-deficient SrCoO2.5-delta

Several different methods have been applied in order to investigate phase r elations in the oxygen-deficient perovskite SrCoO2.5-delta with respect to temperature and oxygen partial pressure. Three different polymorphs of stro ntium cobaltite have been detected: the rhombohedral phase (delta less than or equal to 0.16), the cubic pseudo-perovskite, probably existing in order ed microdomains (0.16 less than or equal to delta less than or equal to 0.2 1) and the disordered cubic perovskite (delta greater than or equal to 0.21 ). The standard thermodynamic functions (enthalpy and entropy) for the corr esponding phase transitions have been calculated. The kinetics of transform ation of cubic pseudo-perovskite --> rhombohedral phase have been studied i n air at different temperatures. (C) 1999 Published by Elsevier Science B.V . All rights reserved.