Structural and electrical properties of selected La_(1-x)Sr_xCo_(0.2)Fe_(0.8)O_3 and La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.6)Ni_(0.2)O_3 perovskite type oxides

摘要

In this paper, the structural and transport properties of selected La_(1-x)Sr_xCo_(0.2)Fe_(0.8)O_3 (LSCF) perovskites and La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.6)Ni_(0.2)O_3 (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_(0.2)Sr_(0.8)Co_(0.2)Fe_(0.8)O_3 (LSCF2828) and La_(0.4)Sr_(0.6)Co_(0.2)Fe_(0.8)O_3 (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.