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

The range of perovskite-type solid solution formation in the system La0.5-xSr0.5-xTi0.6Fe0.4O3-delta in oxidizing conditions is determined from X-ray diffraction and Mossbauer 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-delta. (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). Mossbauer 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.O-4(3-delta) is negligible. (C) 2002 Elsevier Science B.V. All rights reserved.