Native defects, hydrogen impurities, and metal dopants in CeO2

Ceria (CeO₂) is a material of significant technological importance. A detailed understanding of the material's defect physics and chemistry is key to understanding and optimizing its properties. Here, we report a hybrid density-functional study of native point defects, hydrogen impurities, and metal dopants in CeO₂. We find that electron polarons (ηCe^-) and oxygen vacancies (VO²⁺) are the dominant native defects under conditions ranging from extreme oxidizing to highly reducing. Hydrogen is stable either in the hydroxyl (Hᵢ⁺) or hydride (HO⁺) structure, but the substitutional HO⁺ is energetically more favorable than Hᵢ⁺ only under highly reducing conditions. The interstitial Hᵢ⁺ is highly mobile in the bulk. Yttrium (Y) is energetically most favorable at the substitutional Ce site. Copper (Cu) and nickel (Ni) can be incorporated at the substitutional site and/or an interstitial site, depending on actual conditions during preparation, and the dopants can exist in different charge and spin states. In light of the results, we discuss electronic and ionic conduction and the effects of metal doping on the formation of electron polarons and oxygen vacancies.