Crystallographic and compositional analysis of impurity phase U2MoSi2C in UMo alloys

Abstract Impurity phases in metallic nuclear materials can critically influence the microstructural evolution and mechanical properties, making it crucial to understand their structure, composition, and distribution. Using transmission electron microscopy, atom probe tomography, and ab initio calculations, we provide the atomic-scale crystallographic structural and compositional analysis of an impurity phase, U2MoSi2C, in an important nuclear fuel U 10Mo alloy. We identify this phase as having tetragonal symmetry with lattice parameters of a = 6.67 A and c = 4.33 A, and space group P4/mbm (No.127). Ab initio calculations were performed to verify structural stability and to perform atom position refinement.