Structural and electrical properties of selected La1−xSrxCo0.2Fe0.8O3 and La0.6Sr0.4Co0.2Fe0.6Ni0.2O3 perovskite type oxides

In this paper, the structural and transport properties of selected La_1−xSr_xCo_0.2Fe_0.8O₃ (LSCF) perovskites and La_0.6Sr_0.4Co_0.2Fe_0.6Ni_0.2O₃ (LSCFN64262) perovskite are presented. Crystal structure of the samples was characterized by means of X-ray studies with Rietveld method analysis. DC electrical conductivity and thermoelectric power were measured at a wide temperature range (80–1200 K) in air. For La_0.2Sr_0.8Co_0.2Fe_0.8O₃ (LSCF2828) and La_0.4Sr_0.6Co_0.2Fe_0.8O₃ (LSCF4628) perovskites a maximum observed on electrical conductivity dependence on temperature exists at about 750 K. It can be associated with an appearance of oxygen vacancies and implies a mixed ionic-electronic transport. A growing amount of oxygen vacancies at higher temperatures causes a decrease in the electrical conductivity due to a recombination mechanism associated with lowering of the average valence of 3d metals. A similar characteristic was found for LSCFN64262 perovskite, which also exhibits a relatively high electrical conductivity.