Defect structure and oxide ion transport in Sr- and Cr-doped LaCoO 3 − δ

Abstract

The results of oxygen nonstoichiometry, δ, measured by means of coulometric technique as a function of oxygen partial pressure, p o 2, in temperature range 1223 ≤ T, K ≤ 1323 are presented for the perovskite-type doped with chromium solely LaCo 0.7Cr 0.3O 3 − δ and simultaneously doped both with strontium and chromium La 0.7Sr 0.3Co 0.7Cr 0.3O 3 − δ cobaltites. The limit stability of the latter was found to exceed that of undoped cobaltite LaCoO 3 − δ on six orders of magnitude of p o 2 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 La 0.7Sr 0.3Co 0.7Cr 0.3O 3 − δ as a function of oxygen partial pressure p o 2 and temperature in the ranges − 4 ≤ log( p o 2 , atm) ≤ 0 and 1223 ≤ T, K ≤ 1323, respectively. The additional substitution of Sr for La in LaCo 0.7Cr 0.3O 3 − 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 La 0.7Sr 0.3Co 0.7Cr 0.3O 3 − δ were found to be dependent on oxygen partial pressure and nonstoichiometry unlike undoped and doped with chromium lanthanum cobaltites.