Oxidation state of uranium in YxU1-xO2±y solid solution by magnetic susceptibility

Three kinds of Y-U-O solid solutions, such as hypostoichiometric, stoichiometric and hyperstoichiometric, were prepared by the mechanical mixing method and/or coprecipitation method. The process of oxidation of U4+ in UO2 due to the charge neutralization by introduction of Y3+ was studied by magnetic susceptibility measurement. In the range of Y concentrations lower than 50 mol%, U4+ is oxidized to U5+ according to the Y3+ concentration and all of the uranium ions become U5+ at Y = 50 mol%. Further, in Y > 50 mol%, U5+ changes to U6+ and finally all of the uranium ions become U6+ at 66.7 mol% of Y. Through the overall processes from U4+ to U6+ the magnetic susceptibility behavior of the solid solutions turns from the superexchange interaction between U4+ ions to the superexchange interaction between U5+ ions at Y = 50 mol% and finally ends at diamagnetic susceptibility due to both U6+ and Y3+ with the electronic structure of the closed shell. (orig.)