Thermochemical expansion of mixed-conducting (Ba,Sr)Co0.8Fe0.2O3-delta ceramics

Abstract

The thermal and chemical expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and SrCo0.8Fe0.2O3-delta (SCF) mixed ionic-electronic conductors were studied in combination with oxygen nonstoichiometry (delta) at 298-1223 K and p(O-2) = 10(-4) to 1.00 atm. In order to minimize the effects of phase separation or oxygen-vacancy ordering processes, the data were collected in dynamic cooling mode using dense ceramic samples. The procedure was justified by a very fast equilibration at given p(O-2) in high-temperature range demonstrated for ceramics samples with different specific surface area. The difference in nonstoichiometry of BSCF and SCF at temperatures >= 973 K was found to be <= 0.03 oxygen atoms per formula unit. BSCF demonstrates favorably smaller chemical expansion compared to SCF and many other mixed conductors, originating from smaller delta variations and larger unit cell less sensitive to temperature and nonstoichiometry changes. Excessive thermochemical expansion impedes however the use of BSCF in single-phase fuel cell cathodes and planar mixed-conducting membranes. (C) 2013 Elsevier Ltd. All rights reserved.