Oxygen permeability, thermal expansion and stability of SrCo0.8Fe0.2O3-δ-SrAl2O4 Composites

Additions of SrAl2O4 phase to mixed-conducting SrCo0.8Fe0.2O3-delta promote oxygen-vacancy ordering and brownmillerite formation at temperatures below 1050 K due to Al3+ incorporation, but also decrease thermal expansion coefficients (TECs) and improve thermal shock stability. The (SrCo0.8Fe0.2O3-delta SrAl2O4)-Sr-_ composite membranes exhibit also a relatively high stability with respect to interaction with CO, due to A-site deficiency of the perovskite-related phase, caused by partial SrAl2O4 dissolution. The oxygen permeability and electronic conductivity of (SrCo0.8 Fe0.2O3-delta)(1-x)(SrAl2O4)(x) (x=0.3-0.7) composites are determined by the perovskite component and decrease with increasing x. Despite minor diffusion of the transition metal cations into SrAl2O4, hexagonal above 940 K and monoclinic in the low-temperature range, this phase has insulating properties. Nonetheless, at x=0.3 the oxygen permeation fluxes at 1073-1173 are similar to those through single-phase SrCo0.8Fe0.2O3-delta membranes. The average TECs of the composite materials, calculated from dilatometric data in air, vary in the ranges (10.0-11.3) x 10(-6)K(-1) at 300-900 K and (14.7-21.1) x 10(-6) K-1 at 900-1100 K. The low-p(O-2) stability limit and electronic transport properties of SrCo0.8Fe0.2O3-delta are briefly discussed. (c) 2007 Elsevier B.V. All rights reserved.