Local effects of interstitial versus substitutional atoms in $Y2Fe17−xMxAy$ compounds, with $M=Al$ or Si and $A=C$ or N

Interstitial $Y2Fe17−xMxCy$ compounds, with $M=Al$ or Si and $x⩽2,$ $y⩽1,$ were investigated by $Fe57$ Mössbauer spectroscopy at room temperature. In the analysis of the spectra, the preferential occupation by Al or Si of the Fe $(12k)$ sites in the hexagonal $R2Fe17$ phase was taken into account. The hyperfine parameters variations are discussed on the grounds of local crystallographic details at the inequivalent iron sites, altered by the composition modifications. The low values of the isomer shifts and quadrupole interactions suggest small electronic charge redistribution in $Y2Fe17−xMxAy$ as compared to $Y2Fe17.$ However, the isomer shift variations upon Wigner–Seitz cell volume changes evidence for screening and electron transfer effects. In order to provide a more consistent picture of the local effects of interstitial versus substitutional atoms in $R2(Fe,M)17Ay$ compounds, the discussion of the present results is extended to $Fe57$ Mössbauer data obtained on the parent compounds and their nitrides.