NB4N3 - POLYMORPHISM IN CRYSTALLINE NIOBIUM NITRIDES

Local-density-based electronic structure methods are applied to gamma- NbN (tetragonal Nb4N3) to compare it to the strong-coupling supercondu ctor NbN (rocksalt structure) and to the recently proposed Pm3m NbN ph ase, (NbO structure) which has a similar transition temperature. In ce rtain respects gamma-NbN is intermediate between the other phases, as might be expected, but overall the electronic spectrum more closely re sembles rocksalt NbN. The N ion in gamma-NbN is more highly charged (N -1) than in the other two phases.