Oxygen sorption-desorption properties and order-disorder transitions on La-Sr-Co-Fe perovskite-type oxides

The oxygen non-stoichiometry (delta) and structural properties of a brownmillerite-type oxide of La0.1Sr0.9Co0.9-Fe0.1O3-delta (LSCF1991) during oxygen sorption/desorption were investigated by simultaneously applying a temperature-programmed technique and high-temperature X-ray diffraction. The structural changes of perovskite-type (P-type) to brownmillerite-type (B-type) and B-type to P-type occurred within limited p(O-2) ranges, and a B-type phase-stable region was observed in the presence of oxygen at high temperature. Moreover, P-type LSCF1991 changed into B-type LSCF1991 through tetragonal P-type LSCF1991 as an intermediate phase. B-type LSCF1991 showed repeating structural changes with a certain limited p(O-2), which is 0.5% < p(O-2) < 1.0%, whereas such changes could not be observed at p(O-2) > 1.0%. These behaviors correspond with the temperature programmed desorption of oxygen profiles, as well as the amount of lattice oxygen (3-delta). The p(O-2) dependence of the structural change will provide a basis for a further investigation into the durability of an oxygen-permeated membrane by predicting the strain across the membrane under practical conditions. (C)2019 The Ceramic Society of Japan. All rights reserved.