Effect of Manganese Dioxide Addition on the Cubic Phase Stability, Densification and Electrical Conductivity of Scandia-Stabilized Zirconia

Abstract

Zirconia stabilized with 8-12 mol% scandia shows the highest value of oxide ion conductivity among zirconia-based oxides. However, the cubic-rhombohedral phase transition at approximately 600 °C prevents its use as high temperature solid electrolyte. To circumvent this problem, additives have been proposed. In this work, ZrO2:10 mol% Sc2O3 was mixed to MnO2 and sintered at 1200 oC/2 h + 1450 °C/2 h with addition of 1, 1.5, 2 and 2.5 mol% MnO2. All specimens were analyzed by X-ray diffraction for structural phase evaluation and dilatometry for densification. Polished and thermally etched surfaces were observed in scanning electron microscope and scanning probe microscope. Impedance spectroscopy measurements were carried out in the frequency range 5 Hz-13 MHz in the 300-500 oC temperature range. The main results show that the manganese dioxide addition prior to sintering leads to the formation of single cubic phase, to the reduction of the maximum shrinkage temperature, and to an increase in the value of the total oxide ion conductivity.