2018/03/31 by Dawei Zhou, Jiahui Yu, Zhou, Dawei +5
Chemistry · Earth and Planetary Sciences · Materials Science · #Computational Physics (physics.comp-ph) #FOS: Physical sciences #High-pressure geophysics and materials #Materials Science (cond-mat.mtrl-sci) #Nuclear Materials and Properties #Radioactive element chemistry and processing
paper · pdf · doi:10.48550/arxiv.1804.00095
openalex publication_date 2018/03/31 · openalex created_date 2018/04/13 · openalex updated_date 2026/07/28
Uranium nitrides have been the subject of intense research owing to their potential applications as advanced nuclear fuels. However, the phase diagram of the U-N system at low temperature and high pressure still remains unclear. In this paper, we explore extensively the phase diagram of the U-N system up to 150 GPa based on first-principles swarm structure searches. The phase diagrams of the experimentally known stoichiometries like U2N3 and UN2 are refined. At zero temperature and pressure, the experimentally observed CaF2-type UN2 is found to transform into another new I41/amd-type UN2, which is related to the dynamical instability originated from Peierls mechanism. Two new stable high-pressure phases of U2N3 and UN2 are identified for the first time. Besides, several new chemical stoichiometries (UN4, UN3, U3N5 and U2N) are found to have stability fields on the U-N phase diagram. The pressure-induced phase transitions for the U-N system are further investigated. The peculiar structural features such as N2-dimers, planar SO3-like N(N)3 units, non-coplarnar zigzag N4 units, and zigzag U chains are found in U-N compounds under pressure. Our results on the structure exploring provide a better understanding of the structural characteristics and physical properties of uranium nitrides under pressure.