Oxygen nonstoichiometry, thermo-chemical stability and lattice expansion of La0.6Sr0.4FeO3-δ

The oxygen nonstoichiometry of La0.6Sr0.4FeO3-delta was measured at intermediate temperatures (773 to 1173 K) between 1 bar and the decomposition oxygen partial pressure by thermogravimetry and coulometric titration. The decomposition of the ABO(3) perovskite phase was found to occur at low oxygen partial pressures (below 10(-20) bar). Using an atmosphere-controlled high-temperature XRD setup, the rhombohedral lattice parameters were obtained between 10(-4) and 1 bar at 773 to 1173 K. A phase transition from rhombohedral to cubic might be expected to occur at high temperatures and for delta near the plateau at delta = [Sr]/2. The lattice expansion was separated into "pure" thermal and chemically induced expansion by combining the lattice parameters with the oxygen nonstoichiometry data. The linear thermal expansion was formulated with a "pure" thermal expansion coefficient of alpha(th) = 11.052.10(-6) K-1 and a chemical expansion coefficient of alpha(chem) = 1.99-4.10(-2). The results were compared with previous data obtained for La0.6Sr0.4Co1-yFeyO3-delta with y = 0.2-0.8. La0.6Sr0.4FeO3-delta was confirmed to show the highest thermo-chemical stability. While the chemical expansion of La0.6Sr0.4Co1-yFe5O3-delta seems little affected by the iron content, the thermal expansion coefficient was the lowest for La0.6Sr0.4FeO3-delta. (C) 2011 Elsevier B.V. All rights reserved.