New insight in the uranium valence state determination in UyNd1-yO2-x


New insight in the uranium valence state determination in UyNd1-yO2-x

Bes, R.; Kvashnina, K.; Rossberg, A.; Dotavio, G.; Desgranges, L.; Pontillon, Y.; Solari, P. L.; Butorin, S. M.; Martin, P.

The charge compensation mechanisms in UyNd1-yO2-x and its consequence on the overall O stoichiometry (or O/M ratio where M=Nd+U) have been studied through the uranium valence state mixture evolution as a function of Nd content up to y=0.62 by means of high energy resolution fluorescence detection X-ray absorption spectroscopy (HERFD-XAS) at the U M4-edge. Our results clearly demonstrate the formation of U5+ at low Nd content (y < 0.15). Upon increasing the Nd content, oxygen vacancies and the formation of U6+ appear as competing mechanisms for intermediate Nd concentrations, leading to the co-existence of U4+/U5+/U6+ mixed valence and an overall hypostoichiometry (O/M < 2.00). Finally, the formation of U6+ associated with strongly distorted U local environment is observed for high Nd concentrations (y=0.62), leading to an overall hyperstoichiometry (O/M < 2.00)

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Publ.-Id: 26177