Oxide ion transport in undoped and Cr-doped LaCoO3−δ

The results of chemical and self-diffusion coefficient of oxygen vacancies, oxygen ionic conductivity and ionic transport numbers measured as a function of oxygen partial pressure pO2 and temperature in the ranges − 4 ≤ log(pO2, atm) ≤ 0 and 900 ≤ T, °C ≤ 1050, respectively, are presented for the perovskite-type undoped LaCoO3−δ and doped with chromium LaCo0.7Cr0.3O3−δ cobaltites. The dependencies of these properties on oxygen partial pressures were shown to have monotonic character. This can, therefore, indicate that defect clusters or associates containing oxygen vacancies do not form in the oxides over complete pO2 range investigated. The predominant charge carriers in both undoped and Cr-doped lanthanum cobaltite are electron defects, since oxygen vacancies transport numbers do not exceed 2 · 10−3%. The substitution of Cr for Co was found to lead to decrease of both ionic conductivity and oxygen chemical diffusion coefficient. Activation energy of ionic conductivity of the oxides studied decreases with the oxygen nonstoichiometry increase. Self-diffusion coefficient of oxygen vacancies and their mobility were shown to be independent of oxygen partial pressure and nonstoichiometry most likely due to lack of the defects interaction in the oxide studied.