Uranium nitrides have aroused more and more attention due to their unique physical and chemical properties and their excellent performance in applications such as nuclear fuel and anti-corrosion coating for uranium metal. In U-N system, five structures of uranium nitrides, including NaCl-type UN, HgIn-type UN, Mn₂O₃-type α-U₂N₃, La₂O₃-type β-U₂N₃ and CaF₂-type UN₂, have been identified and studied extensively. Up to now, because of the complex nonstoichiometric problems of uranium nitrides, the understanding of the transformation relationship between these phases is still ambiguous. In addition, the basic physical properties of uranium nitrides have been fundamentally changed due to the difference in electronic structures of uranium nitrides with different nitrogen content. The studies of the crystal structure and electronic structure of uranium nitrides are the first step in exploring the causes of their excellent performances, and have attracted much attention in recent years. Based on the analysis and summary of the literatures, as well as the research results of our group, this paper reviews the main progress in the study of the crystal structure and electronic structure of uranium nitrides. The phase transformation and electronic structure evolutions of uranium nitrides are summarized, which is expected to provide reference for the experimental studies and functional applications of uranium nitrides.
Contents
1 Introduction
2 Composition and crystal structure of uranium nitrides
2.1 Crystal structure of UN
2.2 Crystal structure of U₂N₃
2.3 Crystal structure of UN₂
3 Phase relation of uranium nitrides
3.1 Phase relation between NaCl type UN and R3m type UN
3.2 Phase relation between NaCl type UN and U₂N₃
3.3 Phase relation between α-U₂N₃ and β-U₂N₃
3.4 Phase relation between UN₂ and α-U₂N₃
3.5 Phase transition mechanism of uranium nitrides
4 Electronic structures of uranium nitrides
4.1 Electronic structure of UN
4.2 Electronic structure of nitrogen-rich nitrides
5 Conclusion and outlook