Single Cubic Phase Scandia-Stabilized Zirconia: Stabilization and Aging at 600oC

Zirconia stabilized with 8-12 mol% scandia shows the highest value of oxide ion conductivity among zirconia-stabilized oxides. However, the cubic-rhombohedral phase transition at approximately 600°C prevents its use as high temperature solid electrolyte. To circumvent this problem, several additives have been proposed. In this work, ZrO₂:10 mol% Sc₂O₃ was mixed to MnO₂ to evaluate its effect on cubic phase stabilization, oxide ion conductivity and aging at 600^oC. Pressed ceramic pellets of zirconia stabilized with 10 mol% scandia with addition of 1.0, 1.5, 2.0 and 2.5 mol% MnO₂ were sintered at 1500 °C/2 h. X-ray fluorescence analysis was carried out to evaluate the manganese content. In situ high temperature X-ray diffraction data were collected to follow the rhombohedral-to-cubic transition. All specimens were analyzed by X-ray diffraction for structural phase evaluation and dilatometry for monitoring shrinkage. Polished and thermally etched surfaces of the sintered pellets were observed in scanning electron and scanning probe microscopes. Impedance spectroscopy measurements were carried out in the frequency range 5 Hz-13 MHz in the 300-500 °C temperature range. The single cubic structure is achieved for the specimen with 1 mol% MnO₂ nominal addition, with no traces of the rhombohedral phase present in the ScSZ sintered pellets. The oxide ion conductivity of the YSZ + 1 mol%MnO₂ specimen was monitored at 600 ^oC for 100 days by impedance spectroscopy measurements. After an initial decay, the ionic conductivity value of the solid electrolyte remained constant, suggesting its use as solid electrolyte in SOFCs operating at that temperature.