About the event
Speaker: Xiaodong Zhao
Title: Investigation of the Non-ideal Mixing Behavior of U and Th in Orthosilicates
Abstract: Uranothorite (Th1-xUxSiO4) solid solution is of great interest because of its geological relevance and potential applications as a nuclear waste form for actinides. Despite the close cation sizes of U4+ (1.00 Å) and Th4+ (1.05 Å), a non-ideal mixing behavior of the uranothorite was found by calorimetry study. In this talk, I will report our recent study that explained such a non-ideal behavior. Although structural investigation of neutron total scattering revealed a random distribution model for U and Th in the cationic sublattices, further density functional theory (DFT) calculation suggested that partial covalency from the U 5f – O 2p hybridization is removed during mixing, leading to local distortions of UO8 or ThO8 dodecahedra and hence causing the non-ideality.