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), Nb 2 N (hexagonal, β-phase), NbN (hexagonal, ε -phase) and Nb 4 N 3 (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 Nb 2 N (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) → Nb 4 N 3 (tet) → Nb 2 N (hex) were observed by heating in vacuo. Electron diffraction diagrams show the superlattice structures of Nb 2 N (hex) and Nb 4 N 3 (tet). The crystal structure of Nb 2 N (hex) is the same type as that of Nb 2 C. The structure of Nb 4 N 3 (tet), however, is derived from the cubic NaCl type structure of NbN (cub) by the loss of one quarter of nitrogen atoms.