First-Principles Insights into the Oxidation States and Electronic Structures of Ceria-Based Binary, Ternary, and Quaternary Oxides

Ceria and ceria-based materials have versatile technological and industrial applications physically ascribed to the flexible fluctuation of the Ce oxidation state between Ce4+ and Ce3+. Considerable multidisciplinary research has been carried out to obtain the Ce oxidation state, which is crucial for their application; however, a rigorous and physically correct determination of the oxidation state is still lacking. Here, we conduct first-principles DFT + U calculations to unambiguously determine the physical oxidation state of Ce in ceria-based materials, such as homogenous CenO2n–2 (n = 7, 9, 10, 11, and 12), ceria doped by multivalent Ti and V, Ce–Ti(V)–O ternary compounds, and Ce–Ti–V–O quaternary compounds. The results show that the Ce oxidation state depends on the local structure and chemical surrounding: oxygen vacancy facilitates the transition from Ce4+ to Ce3+, which is consistent with the localization of Ce 4f electrons; Ti and V with the 3d energy levels higher than 4f energy levels of Ce gene...