Structural characterization of sputtered single-phase γ‴ iron nitride coatings

Single-phase γ‴-FeN films were deposited by d.c. magnetron sputtering in a reactive Ar/N2 atmosphere. The films were characterized by X-ray diffraction, scanning and transmission electron microscopies, electron energy-loss and Mössbauer spectroscopy. The average lattice parameter of the γ‴ cubic cell is 0.455 nm. Microstructure studies by electron microscopies revealed nanostructured columnar films with no preferential orientation. Diffraction peak intensities (X-ray and electron diffraction) are close to the theoretical values for a ZnS-type structure while profile analysis of the X-ray diffraction pattern using Rietveld refinement method demonstrated that the γ‴-phase is of ZnS-type. The energy-loss near-edge structures of N K-edge of the γ‴-phase is similar to those of the ZnS-type γ″-phase suggesting an identical local atomic environment for N atoms. On the contrary, Mössbauer spectra of both structures are different, which is understood as a consequence of numerous vacancies in the γ‴ structure. Investigations of magnetic properties showed that the γ‴-FeN compound is paramagnetic from room temperature to 2 K. The main conclusion of this work is that the γ‴-FeN phase is of ZnS-type, and not of NaCl-type as it is usually reported.