Structure des Nitrures de Niobium

Abstract

The crystal structure studies of niobium nitrides by electron and X-ray diffraction technique led to the identification of four phases: NbN (cubic, δ-phase), Nb₂N (hexagonal, β-phase), NbN (hexagonal, ε-phase) and Nb₄N₃ (tetragonal, γ-phase). Various methods were used to prepare thin films of Nb nitrides for electron diffraction studies. Firstly, three kinds of oxynitrides, Nb(N,O)I, Nb(N,O)II and Nb(N,O)III were obtained by nitriding the evaporated thin films of Nb in an atmosphere of ammonia. NbN (cub) was formed on heating in vacuo of thin films of Nb(N,O)I, and it was further decomposed into Nb₂N (hex) at a higher temperature. Covering with Nb fine powders makes possible the nitriding of thin films of Nb into NbN (hex). Successive structure transformations NbN (hex) → NbN (cub) → Nb₄N₃ (tet) → Nb₂N (hex) were observed by heating in vacuo. Electron diffraction diagrams show the superlattice structures of Nb₂N (hex) and Nb₄N₃ (tet). The crystal structure of Nb₂N (hex) is the same type as that of Nb₂C. The structure of Nb₄N₃ (tet), however, is derived from the cubic NaCl type structure of NbN (cub) by the loss of one quarter of nitrogen atoms.