Neutron powder-diffraction study of Pr2Fe17 and Pr2Fe17N2.9

Abstract

We report on the effect of nitrogen insertion on the crystal structure of ${\mathrm{Pr}}_2$ ${\mathrm{Fe}}_{17}$. The influence of nitrogen uptake was studied by a neutron powder-diffraction experiment performed at 2, 300, and 655 K. A comparison is made between ${\mathrm{Pr}}_2$ ${\mathrm{Fe}}_{17}$ and the nitride ${\mathrm{Pr}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{N}}_{2.9}$. The nitride is found to retain the host-metal symmetry over the whole temperature range. The nitrogen atoms fill almost completely the site 9e (space group R3m) and their coordination can be described as a distorted octahedron (${\mathrm{Fe}}_4$ ${\mathrm{Pr}}_2$). The change in the environment of the Pr atom induced by nitrogenation is analyzed in terms of the coordination number, bond length, and electronegativity of the nearest surrounding atoms. The values for the magnetic moment of Pr and Fe in ${\mathrm{Pr}}_2$ ${\mathrm{Fe}}_{17}$ and ${\mathrm{Pr}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{N}}_{2.9}$ have been refined in the present work.