Phase identification of iron nitrides and iron oxy-nitrides with Mossbauer spectroscopy

The Mössbauer spectroscopy of all known Fe nitrides is the topic of this paper. Most of the data were accumulated during a study of the growth of the various Fe nitride phases using molecular beam epitaxy of Fe in the presence of a flux of atomic N, or by post-nitriding freshly grown Fe layers also in a flux of atomic N. To get accurate data, most samples were grown with iron enriched in the isotope⁵⁷Fe. Part of the samples were capped in the ultra-high vacuum (UHV) growth facility before exposure to air. By comparing MS data of samples which were capped with that of uncapped samples, we were able to measure the MS components due to oxidation of the nitrides. Also the oxidation behavior at elevated temperatures was studied. This led to a coherent description of the formation of oxy-nitrides as a function of temperature. The UHV conditions during growth and the capping of samples allowed us also to produce for the first time clean samples of Fe nitrides with a composition close to FeN. The phase formation in this composition range is extensively discussed. A fairly complete set of Mössbauer data for all Fe nitride phases and the phases occurring during their exposure to air is presented. This data set may serve to analyze samples of unknown composition, containing Fe nitrides.