Physical and electrochemical characterization of Bi2O3-doped scandia stabilized zirconia

Electrolytes based on Sc₂O₃–ZrO₂ exhibit the highest ionic conductivity of zirconia based systems, however, stabilization of the electrochemical properties at operational temperatures, 600–1000 °C, are needed before implementation into SOFCs. Trace additions of Bi₂O₃ are a known sintering aid for zirconia systems. Crystal structures, electrical properties and long-term stability of Bi₂O₃-doped 10ScSZ systems were investigated. The addition of more than 1.0 mol% Bi₂O₃ resulted in suppression of the rhombohedral to cubic phase transformation at 600 °C and cubic phase stabilization at room temperature. The ionic conductivity of 10ScSZ was also improved by Bi₂O₃ additions. A maximum conductivity of 0.034 S cm⁻¹ at 700 °C was observed in 2 mol% Bi₂O₃-doped 10ScSZ sintered at 1300 °C. No phase change was observed in 10ScSZ after annealing at 1000 °C. A certain amount of monoclinic phase, and dramatic conductivity decrease, were observed in Bi₂O₃-doped samples sintered below 1200 °C after annealing. However, 10ScSZ and 2 mol% Bi₂O₃-doped 10ScSZ sintered at 1300 °C show no significant conductivity degradation with annealing. Samples with more than 1 mol% Bi₂O₃ and sintered above 1300 °C resulted in good ionic conductivity and stability.