Oxygen permeability, thermal expansion and stability of SrCo0.8Fe0.2O3−δ–SrAl2O4 composites
Abstract Additions of SrAl 2 O 4 phase to mixed-conducting SrCo 0.8 Fe 0.2 O 3− δ promote oxygen-vacancy ordering and brownmillerite formation at temperatures below 1050 K due to Al 3+ incorporation, but also decrease thermal expansion coefficients (TECs) and improve thermal shock stability. The SrCo 0.8 Fe 0.2 O 3− δ –SrAl 2 O 4 composite membranes exhibit also a relatively high stability with respect to interaction with CO 2 due to A-site deficiency of the perovskite-related phase, caused by partial SrAl 2 O 4 dissolution. The oxygen permeability and electronic conductivity of (SrCo 0.8 Fe 0.2 O 3− δ ) 1− x (SrAl 2 O 4 ) 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 SrAl 2 O 4 , 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 SrCo 0.8 Fe 0.2 O 3− δ membranes. The average TECs of the composite materials, calculated from dilatometric data in air, vary in the ranges (10.0–11.3) × 10 − 6  K − 1 at 300–900 K and (14.7–21.1) × 10 − 6  K − 1 at 900–1100 K. The low- p (O 2 ) stability limit and electronic transport properties of SrCo 0.8 Fe 0.2 O 3− δ are briefly discussed.