Scandia-stabilized zirconia (SSZ) is a SOFC electrolyte with high oxygen-ion conductivity. It is typically doped with about 8–11 mol% Sc₂O₃ to stabilize the cubic zirconia phase at intermediate SOFC operating temperatures of 650–850°C.However, SSZ has two main limitations. First, it can undergo a cubic-to-rhombohedral phase transition near 580°C. Second, its ionic conductivity gradually decreases over time, a phenomenon known as ageing.

Studies have shown that adding a secondary rare-earth oxide can suppress this phase instability. Co-doped compositions, such as 10Sc1Ce zirconia (10 mol% Sc₂O₃ and 1 mol% CeO₂, ScSZ), help maintain the cubic phase. These materials do not exhibit the undesired phase transformation and show improved structural stability.

Due to its high ionic conductivity, ScSZ can also help clearly resolve performance differences among various electrode materials. This makes it a reliable substrate for comparative electrochemical studies and electrode material screening.