Oxygen permeability and ionic conductivity of perovskite-related La0.3Sr0.7Fe(Ga)O3-δ

The oxygen ionic conductivity of La0.3Sr0.7Fe1-xGaxO3-delta (x = 0.2-0.4), determined by the oxygen permeation, faradaic efficiency, and total conductivity measurements at 1023-1223 K, is essentially independent of oxygen chemical potential and structural changes in the wide oxygen partial pressure range from 10(-14) to 0.21 kPa. At oxygen pressures close to atmospheric air, the ion transference numbers of perovskite-like La0.3Sr0.7Fe(Ga)O3-delta phases vary from 4 x 10(-4) to 4 x 10(-2), increasing with gallium content and temperature. Although there is a great difference between ionic and p-type electronic conductivities in oxidizing atmospheres, the electron-hole conduction was demonstrated to affect oxygen permeation and ambipolar conductivity. In oxidizing conditions, the oxygen permeability of La0.3Sr0.7Fe1-xGaxO3-delta (x = 0-0.4) membranes increase with increasing x. The bulk ionic transport process and surface exchange kinetics both influence the permeation through La0.3Sr0.7FeO3-delta ceramics, whereas the oxygen fluxes through Ga-containing materials are predominantly determined by the bulk ambipolar conduction. Thermal expansion coefficients of La0.3Sr0.7Fe1-xGaxO3-delta (x = 0-0.4) in air vary in the range (11.7-14.9) x 10(6) K-1 at 300-800 K and increase up to (19.5-26.4) x 10(6) K-1 at 800-1170 K. Substitution of iron with gallium was found to suppress both thermal expansion and chemically induced expansion of La0.3Sr0.7Fe(Ga)O(3-)delta materials, originating from oxygen nonstoichiometry variations under changing the oxygen partial pressure. (C) 2002 The Electrochemical Society.