Local structure of uranium in polycrystalline α-U₂N_3+δ film probed by X-ray absorption spectroscopy

Knowledge of the local structure such as U–N interaction is a prerequisite for a better understanding of the physical and chemical properties of nitrogen-rich uranium nitrides. The local structure of U in polycrystalline α-U₂N_3+δ film was investigated by using X-ray absorption spectroscopy at the U L₃ edge combined with spectral calculation using FEFF 9.6 program based on the ab initio multiple scattering theory. The polycrystalline α-U₂N_3+δ sample was shown to be close to U₂N₃ with a narrow distribution of U–N bond lengths. The average valence of U was estimated to be 1.3 and the average bond distance of U–N was determined to be 2.30 Å. The local structure of U in the α-U₂N_3+δ sample can be further specifically expressed by a U₂N₃ model with a lattice parameter of 10.69 (9) Å where U1 atoms are surrounded by nitrogen atoms at ∼2.277, ∼2.295 and ∼2.320 Å.