Nitrogen non-stoichiometric stabilization of UN2

Ab initio quantum chemical calculations are employed to investigate the electronic, mechanical, elastic and thermodynamic properties of UN2. The influence of nitrogen non-stoichiometry on the electronic, structural and dynamical properties of cubic uranium dinitride (UN2) is evaluated. The equilibrium lattice parameters, electronic band structure, density of state (DOS), elastic properties and phonon frequencies for the UN2−x (where x=0, 0.125, 0.25, 0.5) compounds are determined and analyzed in comparison with available experimental data. The introduction of nitrogen vacancies in UN2 structure is accompanied by pronounced DOS changes due to the shifting of the various electronic orbitals as well as the appearance of novel vacancy states in the near-Fermi region. We find that UN1.75, which is a 12.5% nitrogen deficient structure, is observed to be dynamically and elastically stable in good agreement with experimental observations.