Defects clustering and ordering in di- and trivalently doped ceria

The formation and growth of defect clusters in CeO2M 2O3 (M = La3+, Pr3+, Sm 3+, Gd3+, Dy3+, Y3+, Yb 3+) and CeO2DO (N = Cd2+, Ca2+, Sr2+, Ba2+) binary solid solutions have been comparatively studied by atomistic simulations based on energy minimization of atomic interactions. The calculation ensemble, including both divalent and trivalent dopants, shows a similar energetic tendency for defect species (dopants and associated oxygen vacancies) to aggregate and grow. The dumbbell structure has been verified as a universal vacancy structure in oxygen deficient fluorite lattice. Nevertheless, it also demonstrates different tendencies of dopant-vacancy associations that depend on dopant valence and radius. The dopant is site-selective in trivalent defect clusters correlated with dopant size. While in divalent solid solutions, clusters adopt similar dopant-vacancy locations. Furthermore, all clusters in divalently doped ceria have stronger dopant-vacancy associations/interactions compared to those in trivalent ones. As a consequence, the correlation of the dopant size as well as valence effects on oxygen-ion conductivity has been illustrated based on an ordered defect cluster model. This study thereby offers insight into the physical picture of ionic conductivity behavior experimentally obtained in aliovalently doped ceria.