Effects of nitrogen in the (Fe1−xNix)4N compounds (0 ≤x ≤ 0.6)

Single phase γ′-Fe4N-type (Fe1−xNix)4N compounds and Fe1−xNix (0 ≤ x ≤ 0.6) alloys are synthesized and studied by X-ray diffraction and Mössbauer spectroscopy. The structure changes from b.c.c. to f.c.c. when Fe1−xNix (x > 0.25) alloys are nitrided to (Fe1−xNix)4N. The lattice expansion Δa/a is 5.3% for f.c.c. Fe1−xNix alloys (x > 0.25) on nitrogenation. The observed decrease in the average iron hyperfine fields with nitrogenation, amounting to 8 to 14 T, is explained by the volume expansion and the chemical bond effects. The chemical bond effect is about three times larger than the volume effect. The increase in the average isomer shift after nitriding is mainly due to the effect of chemical bounds, which changes the electronic configuration of iron.