Local Structure of Actinide Dioxide Solid Solutions Th_(1-X)U_XO_2 and Th_(1-x)Pu_xO_2

摘要

Extended X-ray absorption fine structure (EXAFS) has been utilized to investigate the local atomic structure around Th,U,and Pu atoms in polycrystalline mixed dioxides Th_(1-X)M_xO_2 (with M = U,Pu) for x ranging from 0 to 1.The composition dependence of the two first-coordination-shell distances was measured throughout the entire composition range for both solid solutions.The first-shell distances vary slightly across the solid-solution composition with values close to those of the pure dioxide parents,indicating a bimodal cation-oxygen distribution.In contrast,the second-shell distance varies strongly with composition,with values close to the weighted amount average distances.Nevertheless,in both systems,the lattice cell parameters,deduced from the first- and second-shell bond determined by EXAFS,are very close to those measured from X-ray diffraction (XRD).They vary linearly with composition,accurately following Vegard's law.