Effects of Nitrogen in the (Fe1-xNix)(4)N compounds (0<=x<=0.6)

Single phase gamma'-Fe4N-type (Fe1-xNix)(4)N compounds and Fe1-xNix (0 less than or equal to x less than or equal to 0.6) alloys are synthesized and studied by X-ray diffraction and Mossbauer spectroscopy. The structure changes from b.c.c. to f.c.c. when Fe1-xNix (x less than or equal to 0.25) alloys are nitrided to (Fe1-xNix)(4)N. The lattice expansion Delta a/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 bonds, which changes the electronic configuration of iron.