Optimization of ionic conductivity in solid electrolytes through dopant-dependent defect cluster analysis

Abstract

Atomistic simulation based on an energy minimization technique has been carried out to investigate defect clusters of R₂O₃ (R = La, Pr, Nd, Sm, Gd, Dy, Y, Yb) solid solutions in fluorite CeO₂. Defect clusters composed of up to six oxygen vacancies and twelve accompanied dopant cations have been simulated and compared. The binding energy of defect clusters increases as a function of the cluster size. A highly symmetric dumbbell structure can be formed by six oxygen vacancies, which is considered as a basic building block for larger defect clusters. This is also believed to be a universal vacancy structure in an oxygen-deficient fluorite lattice. Nevertheless, the accurate positions of associated dopants depend on the dopant radius. As a consequence, the correlation between dopant size and oxygen-ion conductivity has been elucidated based on the ordered defect cluster model. This study sheds light on the choice of dopants from a physical perspective, and suggests the possibility of searching for optimal solid electrolyte materials through atomistic simulations.