Mixed conductivity and Mössbauer spectra of (La0.5Sr0.5)1 — xFe1 — yAlyO3 — d (x = 0 — 0.05, y = 0 — 0.30)

Abstract

Aluminum incorporation in the rhombohedrally distorted perovskite lattice of (Lao.sSro.sJi-.xFe^AlyCb^ (x = 0 -0 .0 5 , у = 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 К increase on doping. The creation o f А-site cation vacancies has an opposite effect on the transport properties of Al-substituted ceramics. The maximum А-site deficiency tolerated by the (La,Sr)(Fe,Al)03_￡ structure is however limited, close to 3-4%. The Mossbauer spectroscopy revealed progressive localization o f 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) i - ,F e 1_>AlJ,O3 _a are (12.2-13.0) x lO ^K " 1 at 300-900K and (20.1-30.0) x 10"6K_I at 900-1200K in air. The steady-state oxygen permeability (OP) of dense Al-containing membranes is determined mainly by the bulk ionic conductivity. The ion transference numbers at 973-1223 К 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. © 2006 Elsevier Inc. All rights reserved.