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 Y 2 O 3 ≥ 8 mol %. Large-scale molecular dynamics simulations further show that ScYSZ at Sc 2 O 3 = 3 mol % and Y 2 O 3 = 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 O v concentration by allowing ⟨111⟩ O v –O v 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.