Neutron-powder-diffraction study of the structure of ${\mathrm{Nd}}_2$${\mathrm{Fe}}_{17}$${\mathrm{N}}_{4.5}$

The crystal and magnetic structure of ${\mathrm{Nd}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{N}}_{4.5}$ at room temperature was refined by Rietveld analysis of neutron-powder-diffraction data. We found that ${\mathrm{Nd}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{N}}_{4.5}$ has a ${\mathrm{Th}}_2$ ${\mathrm{Zn}}_{17}$-type structure (space group R3m) and the nitrogen atoms occupy both 9e and 18g sites with occupancies 0.80 and 0.35, respectively. A physical model is proposed based on the large isotropic thermal factor for the 18g sites.