Ab Initio Molecular Dynamics Study of Electron Excitation Effects on UO(2) and U(3)Si

In this study, an ab initio molecular dynamics method is employed to investigate how the microstructures of UO(2) and U(3)Si evolve under electron excitation. It is found that the U(3)Si is more resistant to electron excitation than UO(2) at room temperature. UO(2) undergoes a crystalline-to-amorphous structural transition with an electronic excitation concentration of 3.6%, whereas U(3)Si maintains a crystalline structure until an electronic excitation concentration reaches up to 6%. Such discrepancy is mainly due to their different electronic structures. For insulator UO(2), once valence U 5f electrons receive enough energy, they are excited to the conduction bands, which induces charge redistribution. Anion disordering is then driven by cation disordering, eventually resulting in structural amorphization. As for metallic U(3)Si, the U 5f electrons are relatively more difficult to excite, and the electron excitation leads to cation disordering, which eventually drives the crystalline-to-amorphous phase transition. This study reveals that U(3)Si is more resistant to electron excitation than UO(2) under an irradiation environment, which may advance the understanding of related experimental and theoretical investigations to design radiation-resistant nuclear fuel uranium materials.