Chemical strain and oxidation-reduction kinetics of epitaxial thin films of mixed ionic-electronic conducting oxides determined by x-ray diffraction

Abstract

X-ray diffraction, at high T's and switching between N2/air atmospheres, was used to compare the chemical expansion due oxygen non-stoichiometry variations between epitaxial films of different mixed ionic-electronic conductors: La0.6Sr0.4CoO3−δ(LSC), Ba0.5Sr0.5Co0.8Fe0.2O3−δ(BSCF), LaNiO3−δ(LNO), La2NiO4+δ(L2NO) and GaBaCo2O5.5+δ(GBCO) and La0.7Sr0.3MnO3−δ(LSM). LSC and BSCF show the largest relative change in the cell parameter Δc/c = +0.5%, while L2NO and GBCO show negative Δc/c = −0.2% and −0.1%, respectively. LNO and LSM show either reduced or negligible chemical expansions. In all cases the values correspond to their particular defect equilibrium and degree of charge localization. The oxygen surface exchange kinetics was also evaluated from in-situ time-resolved analyses of the cell parameter variations. LSC, LNO and GBCO films show fast oxygen reduction kinetics, kchem = 5·10−6, 3·10−6, and 2·10−7 cm/s at 700°C, respectively, in relative agreement with reported values, while BSCF films show much slower kinetics than expected, below kchem = 10−7 cm/s at 650°C, related to the degradation process observed in the films.