Stability and mixed ionic-electronic conductivity of (Sr,La)(Ti,Fe)O3-δ perovskites

Doping of cation-stoichiometric and A-site-deficient perovskites LaxSr1-xTi1-yFeyO3 (- delta) and LaxSr0.90 - x Ti0.60Fe0.40O3 (-) (delta) (0 less than or equal to x less than or equal to 0.45, 0.40 less than or equal to y less than or equal to 0.80) with lanthanum leads to a greater stability with respect to reduction in H-2-containing atmospheres and the reaction with yttria-stabilised zirconia (YSZ). Partial oxygen ionic and p-type electronic conductivities in air as well as thermal expansion decrease with lanthanum content, whilst the effect on the n-type conduction in reducing environments is opposite. The ion transference numbers of (Sr,La)(Ti,Fe)O-3 (-) (delta), determined by faradaic efficiency measurements in air at 800-1000degreesC, vary from 1 x 10(-4) to 4 x 10(-2), increasing when temperature increases. Deficiency of the A sublattice and increasing iron concentration in the B sublattice result in a higher thermal expansion and greater reducibility; the reactivity with YSZ can be suppressed by the creation of A-site vacancies. The ionic and p-type electronic conductivities were both found to decrease with A-site deficiency and to increase with Fe content. The average thermal expansion coefficients of (Sr,La)(Ti,Fe)O3 -delta in air at 100-850 degreesC are in the range (10.6-21.5) x 10(-6) K-1. (C) 2003 Elsevier Science B.V All rights reserved.