Redox behavior and transport properties of La0.5−xSr0.5−xFe0.4Ti0.6O3−δ (0<x<0.1) validated by Mössbauer spectroscopy

The range of perovskite-type solid solution formation in the system La0.5−xSr0.5−xTi0.6Fe0.4O3−δ in oxidizing conditions is determined from X-ray diffraction and Mössbauer spectroscopy data to correspond to approximately 0–10% of the A-site concentration, similar to other numerous perovskite systems. Reduction and subsequent reoxidation of the oxides leads to a narrowing of this range and the segregation of the hematite phase at x=0.05. Increasing A-site deficiency results in the formation of oxygen vacancies and decreasing stability in reducing environments. The total conductivity of La0.5−xSr0.5−xTi0.6Fe0.4O3−δ (x=0.02–0.10) ceramics is essentially independent of composition in air and increases with increasing x in reducing atmospheres, due to increasing concentrations of n-type charge carriers and the formation of metallic iron. Partial decomposition of the perovskite phase in hydrogen, resulting in metal Fe formation, was found to be reversible when the A-site deficiency is small (x<0.05). Mössbauer spectroscopic data showed that, contrary to other perovskite-type titanates–ferrites, the concentration of Fe4+ cations in the perovskite lattice of oxidized La0.5−xSr0.5−xTi0.6Fe0.4O3−δ is negligible.