The equilibrium O content was measured in Sr0.6La0.4CoO3, at 650 to 900C, under O partial pressure ranging from 10-5 to 1atm. The data were used to deduce changes, in the partial entropy and enthalpy of O in the solid, as a function of the O content. It was shown that the initially cubic perovskite underwent a phase transition, to a tetragonal structure, in Sr0.6La0.4CoO2.7 and lower O stoichiometries. The O permeation of Sr0.6La0.4CoO3, at 700 to 900C, was found to be controlled by bulk solid-state processes. The activation energy was equal to about 0.8eV at high O pressures and low O non-stoichiometries. An increasing O deficiency resulted in a rapid increase in the activation energy. Together with thermodynamic data, these changes could be explained as resulting from the intrinsic spatial inhomogeneity in O-vacancy distribution, which varied with both temperature and the O non-stoichiometry. It was shown that, when the O-deficiency increased at constant temperature, the O vacancies formed themselves into locally ordered micro-domains (clusters). This eventually resulted in a transformation of the cubic perovskite structure into the tetragonal structure. The O-ion conductivity depended strongly upon the development of the ordering.

Oxygen Thermodynamics and Ion Conductivity in the Solid Solution (La,Sr)CoO3 at Large Strontium Content. M.V.Patrakeev, I.A.Leonidov, E.B.Mitberg, A.A.Lakhtin, V.G.Vasiliev, V.L.Kozhevnikov, K.R.Pöppelmeier: Ionics, 1999, 5[5-6], 444-9