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 degrees 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 1.0mol% Bi2O3 resulted in suppression of the rhombohedral to cubic phase transformation at 600 degrees 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 degrees C was observed in 2 mol% Bi2O3-doped 10ScSZ sintered at 1300 degrees C. No phase change was observed in 10ScSZ after annealing at 1000 degrees C. A certain amount of monoclinic phase, and dramatic conductivity decrease, were observed in Bi2O3-doped samples sintered below 1200 degrees C after annealing. However, 10ScSZ and 2 mol% Bi2O3-doped 10ScSZ sintered at 1300 degrees C show no significant conductivity degradation with annealing. Samples with more than 1 mol% Bi2O3 and sintered above 1300 degrees C resulted in good ionic conductivity and stability. (c) 2007 Elsevier B.V. All rights reserved.