Influence of cerium doping on mechanical properties of tetragonal scandium-stabilized zirconia

Mechanical properties of tetragonal scandium-stabilized zirconium oxide (ScSZ) co-doped with cerium oxide are studied before and after a complete reduction of Ce4+ to Ce3+. Samples of 6Sc1CeSZ (i.e., 6 mol% Sc2O3, 1 mol% CeO2), 6Sc2CeSZ, and 4Sc1CeSZ are produced by pressure-less sintering in air at 1450 °C. Test pieces are annealed at 1200 °C in an atmosphere of forming gas (5% H2, 95 % N2). Vickers hardness, Young's modulus, 4-point bending strength, and fracture toughness are measured at room temperature. Values of hardness and Young's modulus are similar for different compositions of ScSZ:Ce and stay practically unaffected by the reduction. Both the fracture toughness and strength significantly decrease and the largest drop is measured for the 6Sc2CeSZ, having the highest concentration of cerium. The observed degradation of mechanical properties suggests that cerium-free electrolytes should be preferred for the fabrication of the electrolyte-supported planar SOFCs.