Mixed conductivity and Mössbauer spectra of (La0.5Sr0.5)1−xFe1−yAlyO3−δ (x=0-0.05, y=0-0.30) |
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Authors: | Vladislav V. Kharton Joao C. Waerenborgh Sergey O. Yakovlev Piotr Gaczyński Aleksey A. Yaremchenko Victor V. Samakhval |
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Affiliation: | a Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal b Institute of Physicochemical Problems, Belarus State University, 14 Leningradskaya Street, 220050 Minsk, Belarus c Chemistry Department, ITN/CFMC-UL, Estrada Nacional 10, P-2686-953 Sacavém, Portugal d Institute of Solid State Chemistry, Ural Division of RAS, 91 Pervomaiskaya Street, Ekaterinburg 620219, Russia |
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Abstract: | Aluminum incorporation in the rhombohedrally distorted perovskite lattice of (La0.5Sr0.5)1−xFe1−yAlyO3−δ (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−δ structure is however limited, close to 3-4%. The Mössbauer 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−xFe1−yAlyO3−δ are (12.2-13.0)×10−6 K−1 at 300-900 K and (20.1-30.0)×10−6 K−1 at 900-1200 K 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 K in air, calculated from the oxygen permeation and faradaic efficiency (FE) data, vary in the range 1×10−4-3×10−3, increasing with temperature. |
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Keywords: | Lanthanum-strontium ferrite Perovskite Mixed conductor Oxygen ionic conductivity Electronic transport Mö ssbauer spectroscopy |
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