EFFECTS OF NITROGEN IN THE (FE1-XNIX)(4)N COMPOUNDS LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-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 synthes ized 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 expa nsion Delta a/a is 5.3% for f.c.c. Fe1-xNix alloys (x > 0.25) on nitro genation. The observed decrease in the average iron hyperfine fields w ith nitrogenation, amounting to 8 to 14 T, is explained by the volume expansion and the chemical bond effects. The chemical bond effect is a bout three times larger than the volume effect. The increase in the av erage isomer shift after nitriding is mainly due to the effect of chem ical bonds, which changes the electronic configuration of iron.