A comparative study of high temperature properties of cobalt-free perovskites

Co-free perovskites with chemical composition Ba_0.5Sr_0.5Fe_0.8M_0.2O_3-δ (M = Ni, Cu, Zn) were synthesized by the modified Pechini method, and their structure and microstructure were characterized by XRD and SEM. Oxygen content, electrical resistivity and Thermal Expansion Coefficient (TEC) were evaluated in air between room temperature and 900 °C. The high-temperature properties of these perovskites were compared with those of Co containing Ba_0.5Sr_0.5Fe_0.8Co_0.2O_3-δ perovskite. The highest electrical conductivity was obtained for Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3-δ, with values of 47.6 Scm^?1 at 544 °C. This same composition also exhibits the highest oxygen vacancies concentration: 3-δ = 2.61 at room temperature. In contrast, the Ba_0.5Sr_0.5Fe_0.8Zn_0.2O_3-δ, showed lower electrical conductivity suggesting that the Zn⁺² ions block electron transport. Co-free perovskites seem to be stable at high temperatures for long term periods. However, these compounds suffered degradation at room temperature in samples stored in air.