Scandia as the Oxygen Vacancy Stabilizer to Boost the Ionic Conductivity of Sc–Y-Codoped Zirconia

Scandia (Sc) and yttria (Y) codoped zirconia (ScYSZ) emerged as a promising candidate for high-performance solid electrolyte materials utilized in intermediate-temperature solid oxide fuel cells (IT-SOFCs). While it exhibits a record-high ionic conductivity (∼0.10 S/cm at 800 °C), the physical origin of the superior performance remains poorly understood, limiting the further optimization and the application in IT-SOFC. Here, we construct the Sc–Y–Zr–O global neural network potential and explore systematically the thermodynamic landscape of ScYSZ across 65 different compositions (6.7–14.3 mol % dopants). From millions of candidate structures, we identify a thermodynamically stable cubic phase region at Sc/Y < 1 with Y2O3 ≥ 8 mol %. Large-scale molecular dynamics simulations further show that ScYSZ at Sc2O3 = 3 mol % and Y2O3 = 8 mol % yields an exceptional ionic conductivity of 0.13 S/cm at 800 °C, surpassing conventional 8 mol % Y-stabilized zirconia (YSZ) by an order of magnitude. Our analysis reveals that the presence of Sc not only increases the Ov concentration by allowing ⟨111⟩ Ov–Ov pairs but also reduces the oxygen migration barriers markedly. Our results not only pinpoint the optimal ScYSZ composition for IT-SOFC applications theoretically but also establish a general framework for the rational design of advanced solid electrolyte materials.