Phase Transformation of Yttria-Stabilized Zirconia (3 mol% Y2O3) in Fuel Cell Caused by Manganese Diffusion

The diffusion coefficient of Mn in yttria-stabilized zirconia (YSZ, 3 mol%Y2O3) and the structural change in YSZ have been investigated. The diffusion coefficients of Mn were determined to be 7×10−14 m2/s at 1573 K and 2×10−13 m2/s at 1673 K by analyzing the concentration profiles of Mn in YSZ/Mn3O4 diffusion couples. The solubilities of MnOx were 7.4 mol% and 7.6 mol% at 1573 and 1673 K, respectively. Remarkable grain growth was observed on the YSZ side near the interface. The dissolution of MnOx almost up to the solubility limit of 7.6 mol% resulted in grain growth and the phase transformation from the tetragonal phase to the fluorite-type cubic phase. These results were discussed by comparing with the previous studies on the ZrO2–Y2O3–MnOx ternary system and on the ZrO2–MnO binary system.