Microstructural Effects on the Oxygen Exchange Kinetics of La0.7Sr0.3MnO3 Thin Films

We investigated the relative contribution of the native surface and of the grain boundaries intersecting the surface to the chemical surface exchange of La0.7Sr0.3MnO3 (LSM) thin films. The chemical surface exchange coefficients, k(chem), were determined using electrical conductivity relaxation (ECR). Two k(chem) values were obtained, indicating two surface exchange processes occurred in parallel. These two k(chem) values had different activation energies (E-a), which were interpreted as belonging to (1) the native surface response of individual grains/variants and (2) the variant / grain boundaries of the textured films. The first process has an activation energy of E-a,E-1 approximate to 1.57 eV, while (Ea,2) approximate to 0.87 eV. The k(chem,2) values are almost 3 orders of magnitude higher than the k(chem,1) values at low temperatures. At higher temperatures, the data can be fit with one k(chem) that has an intermediate value of E-a, indicative of a transition region.