Insight on the oxidation resistance of UOxNy layers: A density functional study

Abstract CaF 2 -type UN x O y layers prepared by the nitriding of depleted uranium metal exhibit good oxidation resistance; however, the mechanism is still lacking. This study examined the effect of O on extrinsic point defects in UN 2 using density functional calculations. The calculations reveal that N vacancy easily forms in CaF 2 -type UN 2 , and O atom lowers the formation energy of N vacancy. By gradually replacing N atoms with O atoms, a series of U–N–O ternary compounds with various N:O ratios, which are not only energetically stable but also mechanically stable within both GGA and GGA+ U frameworks, have been found. Additionally, full U–N bonding states contributes more to stabilize the crystal system than the partial U–O bonding states. Collectively, these calculations predict the existence of U–N–O ternary compounds, some of which cannot be distinguished from UN 2 by regular X-ray diffraction. Present calculations show that the oxidation resistance of UN x O y layers may be related to U–N–O ternary compounds with various N:O ratios, and suggest further comparative exploration of the adsorption and diffusion of O atoms on the surface of typical ternary compounds, UN 2 and UN.