Oxygen nonstoichiometry, thermo-chemical stability and lattice expansion of La 0.6Sr 0.4FeO 3 − δ

Abstract

The oxygen nonstoichiometry of La 0.6Sr 0.4FeO 3 − δ 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 δ near the plateau at δ = [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 α th = 11.052 · 10 − 6 K − 1 and a chemical expansion coefficient of α chem = 1.994 · 10 − 2 . The results were compared with previous data obtained for La 0.6Sr 0.4Co 1 − y Fe y O 3 − δ with y = 0.2–0.8. La 0.6Sr 0.4FeO 3 − δ was confirmed to show the highest thermo-chemical stability. While the chemical expansion of La 0.6Sr 0.4Co 1 − y Fe y O 3 − δ seems little affected by the iron content, the thermal expansion coefficient was the lowest for La 0.6Sr 0.4FeO 3 − δ .