Ionic conductivity of stabilized zirconia-scandia-europia

Scandia-doped zirconia is a well-known solid solution exhibiting the highest ionic conductivity among zirconia-based solid electrolytes. The main concern related to this solid solution is the reversible cubic-to-rhombohedric... [ view full abstract ]

Scandia-doped zirconia is a well-known solid solution exhibiting the highest ionic conductivity among zirconia-based solid electrolytes. The main concern related to this solid solution is the reversible cubic-to-rhombohedric phase transition at 600°C. The rhombohedric phase has lower ionic conductivity, avoiding the application of this solid electrolyte at intermediate temperatures (500-700°C) in electrochemical devices, such as solid oxide fuel cells. Stabilization of the high-temperature cubic phase may be accomplished by addition of a second dopant. In this context, several rare earth oxides have demonstrated to be effective for stabilization of the cubic phase at room temperature in the zirconia-scandia system. In this work, small amounts (up to 1.25 mol%) of europium oxide were added to zirconia-10 mol% scandia. The specimens were sintered at 1500°C and characterized by X-ray diffraction, differential scanning calorimetry and impedance spectroscopy. In the low-temperature range (below 600°C), all double doped specimens show higher grain conductivity than the parent solid electrolyte (ZrO₂: 10 mol% Sc₂O₃). The cubic phase was fully stabilized at room temperature for specimens containing at least 1.0 mol% Eu₂O₃. Differential scanning calorimetry measurements evidence a gradual decrease of the temperature and of the energy for phase transition for increasing amount of europium oxide. The dependence of the ionic conductivity on the temperature shows a deviation of the slope at 600°C towards lower activation energy values.