Defect structure and oxide ion transport in Sr- and Cr-doped LaCoO3 − δ

The results of oxygen nonstoichiometry, δ, measured by means of coulometric technique as a function of oxygen partial pressure, po2, in temperature range 1223 ≤ T, K ≤ 1323 are presented for the perovskite-type doped with chromium solely LaCo0.7Cr0.3O3 − δ and simultaneously doped both with strontium and chromium La0.7Sr0.3Co0.7Cr0.3O3 − δ cobaltites. The limit stability of the latter was found to exceed that of undoped cobaltite LaCoO3 − δ on six orders of magnitude of po2 at a given temperature. The modeling of the defect structure of these perovskites was carried out and its adequate model was found. Chemical and self-diffusion coefficients of oxygen vacancies and oxygen ionic conductivity and ionic transport numbers were measured for the first time for La0.7Sr0.3Co0.7Cr0.3O3 − δ as a function of oxygen partial pressure po2and temperature in the ranges − 4 ≤ log(po2, atm) ≤ 0 and 1223 ≤ T, K ≤ 1323, respectively. The additional substitution of Sr for La in LaCo0.7Cr0.3O3 − δ was shown to lead to noticeable increase of ionic conductivity and oxygen chemical diffusion coefficient at given values of oxygen partial pressure and temperature as compared to lanthanum cobaltite doped with chromium solely. Self-diffusion coefficient of oxygen vacancies and their mobility in La0.7Sr0.3Co0.7Cr0.3O3 − δ were found to be dependent on oxygen partial pressure and nonstoichiometry unlike undoped and doped with chromium lanthanum cobaltites.