Mixed conductivity and Mossbauer spectra of (La0.5Sr0.5)(1-x)Fe1-gamma Al gamma O3-delta (x=0-0.05, gamma=0-0.30)

摘要

Aluminum incorporation in the rhombohedrally distorted perovskite lattice of (La0.5Sr0.5)(1-x)Fe1-yAlyO3-delta (x = 0-0.05, y = 0-0.30) decreases the unit Cell volume and partial ionic and p-type electronic Conductivities, while the oxygen nonstoichiometry and thermal expansion at 900-1200 K increase on doping. The creation of A-site cation vacancies has an opposite effect on the transport properties of Al-substituted ceramics. The maximum A-site deficiency tolerated by the (La,Sr)(Fe,Al)O3-delta Structure is however limited, close to 3-4%. The Mossbauer spectroscopy revealed progressive localization of electron holes and a mixed charge-compensation mechanism, which results in higher average oxidation state of iron when Al3+ concentration increases. The average thermal expansion coefficients of (La0.5Sr0.5)(1-x)Fe1-yAlO3-delta are (12.2-13.0) x 10(-6) K-1 at 300-900 K and (20.1-30.0) x 10(-6) K-1 at 900-1200 K in air. The steady-state oxygen permeability (OP) of dense Al-containing membra ties is determined mainly by the bulk ionic conductivity. The ion transference numbers at 973-1223 K in air, calculated from the oxygen permeation and faradaic efficiency (FE) data, vary in the range 1 X 10(-4)-3 x 10(-3), increasing with temperature. (c) 2006 Elsevier Inc. All rights reserved.