Chemical compatibility of perovskite-type oxide La0.7Ca0.3Cr1-yCoyO3 with Y2O3 stabilized ZrO2

Article abstract of DOI:10.1016/0025-5408(95)00062-3

In order to evaluate the compatibility between the SOFC (Solid Oxide Fuel Cells) interconnector material of the perovskite-type La_0.7Ca_0.3Cr_1-yCo_yO₃ (y = 0.05, 0.1 and 0.2) and 8 mol%Y₂O₃-ZrO₂ (YSZ), two types of experiments were carried out in air. One was by the reaction of powder mixtures. The reaction products were identified by X-ray analysis after heating at 1000-1300 °C. The other was the experiments using diffusion couples. The distribution of elements at the interface was observed by EPMA for the couples heated at 1300 °C and 1400 °C. The reaction progressed mainly by the dissolution of calcium ions from the perovskite phase into YSZ. In the perovskite phase, due to the loss of A-site Ca ion, the activity of B-site ions increased, resulting in the deposition of the spinel-type CoCr₂O₄. The excess amount of calcium ions incorporated in YSZ reacted ZrO₂ to form CaZrO₃. Increase of cobalt content enlarge the reactivity of the perovskite phase with YSZ. The parabolic rate constant of the reaction, k_p, was determined by the thickness of CaZrO₃ at the interface of the diffusion couples. Calculated k_p were 2.9×10^-12cm²sec^-1 and 2.1×10^-11cm²sec^-1 at 1300 °C and 1400 °C, respectively. For the practical application as the SOFC interconnector material, the content of cobalt as a sintering accelerator in (La, Ca)CrO₃ must be controlled at low level to keep the chemical interaction to a minimum.