Differential interplay between Ce and U on local structures of U_1-xCe_xO₂ solid solutions probed by X-ray absorption spectroscopy

Uranium–cerium mixed oxides U_1-xCe_xO₂ (x = 0.05, 0.20, 0.35, 0.50, 0.65, 0.80) were synthesized by co-precipitation method. The U_1-xCe_xO₂ samples were confirmed to be solid solutions with lattice parameters following Vegard's law by using X-ray diffraction technique combined with X-ray absorption spectroscopy. The effects of cerium content on the local structures of U and Ce in the U_1-xCe_xO₂ solid solutions were further studied by extended X-ray absorption fine structure (EXAFS) at the U L₃ edge and Ce K edge, respectively. Significantly, the local disorder degree around U and Ce in the U_1-xCe_xO₂ were found to be not equivalent. There is differential interplay between U and Ce on the local structures of the U_1-xCe_xO₂. The order degree in the local structure of U increases with the content of cerium when the Ce content is kept about 35% or more. In contrast, the disorder degree in the local structure of Ce increases with U content once uranium is added into CeO₂.