Reactions between La1-xCaxMnO3 and CaO-stabilized ZrO2 - Part II - Diffusion couples

The chemical stability of diffusion couples and coarse grain powder mixture s of calcium substituted lanthanum manganite and cubic calcia stabilized zi rconia have been studied. The aim was to investigate the chemical stability of these materials as a model system for respectively the cathode and the electrolyte in solid oxide fuel cells. With increasing amount of Ca in lant hanum manganite, the major secondary phase was shifted from La2Zr2O7 to CaZ rO3, and the thickness of the reaction layers of secondary phases was incre asing with increasing heat treatment time. Precipitation of La2O3 had taken place in the perovskite containing low amounts of Ca (0 and 20 mol %). The transport mechanisms of the cations were strongly dependent on the interfa ce geometry. La0.7Ca0.3MnO3 was observed to give the most stable interface to zirconia both in air and in reducing atmosphere (p(O) similar to 10(-)6 atm). A-site deficiency of LaMnO3 was also observed to increase the stabili ty. However, we conclude that a thin film of an electrode material consisti ng of lanthanum manganite on a zirconia substrate is unstable, regardless o f A-site deficiency, because the solubility limit of Mn in the zirconia is not reached. From the experimental data, a reaction mechanism has been prop osed, based on observations of relative diffusion rates. (C) 1999 Kluwer Ac ademic Publishers.