Structure of TiN x studied by electron diffraction and microscopy

Abstract

The crystal and internal structures of the non-stoichiometric compound TiNx (x = 0.61~0.999, δ-phase, NaCl type) have been studied by electron diffraction and microscopy. In general, interstitial N atoms produce only short-range order, but in TiN0.61 there is long-range order after aging at 500°C for one or three months. The ordered structure is tetragonal with lattice parameters a = 4.198 Å < a 0, and c = 8.591 Å > 2a 0 (a 0 = 4.221 Å: lattice parameter of disordered TiN0.61), and belongs to the space group I41/amd with the atom positions 8 Ti at 8(e) with z = ¼+0.018, 4 N at 4(a) and 0.88 N at 4(b). The ordered regions develop from small isolated regions and coalesce gradually with aging. The resulting structure contains antiphase and semi-antiphase domain boundaries with respect to the N atom arrangement. The appearance of the semi-antiphase domain boundaries is due to the structure being able to have both 41 and 43 screw axes. The structural difference between TiN x and γ (or ∊)-Ti2N is also discussed.