Neutron diffraction study of the perovskite-type lanthanum cobaltite La0.6Sr0.4Co0.8Fe0.2O3-δ at 1260 °C and 394 °C

Crystal structure of a perovskite-type strontium- and iron-co-doped lanthanum cobaltite, La0.6Sr0.4Co0.8Fe0.2O3-delta (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 degrees C and 1260 degrees C. The LSCF6482 was trigonal R (3) over barc at 394 degrees C, and cubic Pm (3) over barm at 1260 degrees C. The refined occupancies of O atom were 1.0 and 0.904(6) at 394 degrees C and 1260 degrees C, respectively. At 1260 degrees C the oxygen deficiency 6 in La0.6Sr0.4Co0.8Fe0.2O3-delta was estimated to be delta=0.288(15), indicating an average valence of +2.8 for the B-site Co0.8Fe0.2 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 degrees C, comparing at 394 degrees C. A curved path for oxide-ion migration between adjacent anion sites in LSCF6482 was suggested at 1260 degrees C, although it was not observed as a connected density in the experimental mapping. (C) 2008 Elsevier B.V. All rights reserved.