Phase transformations in nearly stoichiometric NbNx

• Published in: Journal of applied physics 1976-07, Vol.47 (7), p.2833-2840
• Main Authors: Oya, Gin-ichiro, Onodera, Yutaka
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.323080

Processes of the phase transformation in nearly stoichiometric niobium nitride, from cubic δ-NbN to hexagonal ε-NbN, are studied by selected-area electron diffraction, by using NbNx films of the transition state prepared by annealing δ-NbNx films at about 1000 °C in an atmosphere of H2 gas. The diffraction patterns taken from the annealed NbNx films suggest that the phase transformations (vacancy-poor-) δ-NbNx (cub.) → (N-vacancy-) ordered δ-NbN (tet.)  → ordered ζ-NbN (hex.)  → ordered γ′-NbN (mon.)  → δ′-NbN (hex.)  → ε-NbN (hex.) occur. Ordered δ-NbN, ordered ζ-NbN, ordered γ′-NbN, and δ′-NbN are transient phases which occur during the transformation δ-NbNx → ε-NbN, and the superlattice structures of the three ordered phases are described by the ordering of N vacancies with random Nb vacancies in their fundamental lattices. Mechanisms of the transformations from δ-NbNx to ε-NbN at about 1000 °C are discussed on the basis of the transient phases observed during the phase transformations.