Substrate and Thickness Effects on the Oxygen Surface Exchange of La0.7Sr0.3MnO3 Thin Films
journal contributionposted on 23.05.2012, 00:00 by Lu Yan, Paul A. Salvador
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Substrate- and thickness-related effects on the oxygen surface exchange of La0.7Sr0.3MnO3 (LSM) thin films were investigated to understand better cathode reactivity in solid oxide fuel cells. Epitaxial (100)-oriented LSM films were fabricated on (100)-SrTiO3 and (110)-NdGaO3 substrates and were characterized using electrical conductivity relaxation. A strong substrate effect on the chemical surface exchange coefficient (kchem) was observed, with a higher kchem found for films on SrTiO3 than those on NdGaO3. Two distinct activation energies (Ea) were observed for kchem, which were assigned to two parallel exchange processes; the relative contributions from each depended on the substrate, film thickness, and temperature. For films coherently strained to the substrates, kchem values differed by almost an order of magnitude, whereas Ea was ∼1.5 (± 0.1) eV on both substrates. For relaxed films, kchem values differed only by a factor of 2, and Ea was ∼0.75 (± 0.1) eV on both substrates. We discuss the strain effect relative to the native surface exchange and the thickness effect relative to the extended defect populations in the films. The outcome of this study sheds light on how microstructural features affect surface chemistry in modified cathodes.