Neutron diffraction study of the perovskite-type lanthanum cobaltite La 0.6Sr 0.4Co 0.8Fe 0.2O 3 − δ at 1260 °C and 394 °C

Abstract

Crystal structure of a perovskite-type strontium- and iron-co-doped lanthanum cobaltite, La 0.6Sr 0.4Co 0.8Fe 0.2O 3 − δ (LSCF6482) has been studied by Rietveld analysis, maximum-entropy method (MEM) and MEM-based pattern fitting of in situ neutron powder diffraction data measured in air at 394 °C and 1260 °C. The LSCF6482 was trigonal R3¯ c at 394 °C, and cubic Pm3¯ m at 1260 °C. The refined occupancies of O atom were 1.0 and 0.904(6) at 394 °C and 1260 °C, respectively. At 1260 °C the oxygen deficiency δ in La 0.6Sr 0.4Co 0.8Fe 0.2O 3 − δ was estimated to be δ = 0.288(15), indicating an average valence of + 2.8 for the B-site Co 0.8Fe 0.2 cations. Refined anisotropic atomic displacement parameters and nuclear density mapping reveal that the oxide ions in LSCF6482 exhibit a large thermal motion perpendicular to the (Co,Fe)–O bond at 1260 °C, comparing at 394 °C. A curved path for oxide-ion migration between adjacent anion sites in LSCF6482 was suggested at 1260 °C, although it was not observed as a connected density in the experimental mapping.