Structure and Stability of Nonstoichiometric Cubic Phase δ-NbN1.2(O, C)

Abstract

The nonstoichiometric δ-niobium nitride with surplus content of nitrogen atoms and the NaCl-type structure (a = 0.439 nm), i.e. δ-NbN1.2(O, C), is stabilized in epitaxial deposited films. The diffraction patterns of these films display intensive diffuse scattering with regular intensity vanishings in the form of plane regions in the vicinity of structural and superstructural reciprocal space points of the δ-phase and in the form of spherical surfaces in the neighbourhood of structural points. The analysis performed shows that this scattering can be associated with the presence of mixed-nature short-range order regions in the nonstoichiometric δ-NbN1.2(O, C) phase which are characterized by longitudinal uncorrelated atomic displacement waves, as well as by concentration-type waves. The ordered oxycarbonitride phase (X-phase) described in the first approximation by the cubic lattice with parameter a = 0.392 nm is found to precipitate when annealing the films at T = 873 K. It has been established that the diffuse scattering occurring in δ-NbN1.2(O, C) and the structure of shortrange order regions exhibit certain correlation with the structure of the precipitated ordered phase — G100x ≈ 1.1G100δ = K1; G010x ≈ 1.1G010δ = K2 (where K1 and K2 are wave vectors of longitudinal atomic displacement waves characterizing short-range order). [Russian Text Ignored]