Electrical conductivity enhancement in heterogeneously doped scandia-stabilized zirconia

Composites of 6 mol% scandia-stabilized zirconia materials (6ScSZ) and nanosize Al2O3 powder (0–30 wt.%) were prepared and characterized for electrical conductivity by the ac impedance method at various temperatures ranging from 300 to 950 °C. All the composites characterized showed improved conductivity at higher temperatures compared to the undoped ScSZ. An average conductivity of 0.12 S cm−1 was measured at 850 °C for 6ScSZ + 30 wt.% Al2O3 composite samples, an increase in conductivity up to 20% compared to the undoped 6ScSZ specimen at this temperature. Microstructural evaluation using scanning electron microscopy revealed that the ScSZ grain size was relatively unchanged up to 10 wt.% of Al2O3 additions. However, the grain size was reduced in samples with higher (20 and 30 wt.%) additions of Al2O3. Small grain size, reduced quantity of the 6ScSZ material (only 70%), and improved conductivity makes these ScSZ + 30 wt.% Al2O3 composites very attractive as electrolyte materials in view of their collective mechanical and electrical properties and cost requirements. The observed increase in conductivity values with the additions of an insulating Al2O3 phase is explained in light of the space charge regions at the 6ScSZ–Al2O3 grain boundaries.