An ab initio study of nickel substitution into iron

Ab initio calculations at 0 K have been used to predict the effect of nickel on the phase stability of the body-centred-cubic (bcc), face-centred-cubic (fcc) and hexagonal-close-packed (hcp) phases of iron. We have calculated the relative stability of hcp-Fe in the ferromagnetic and two antiferromagnetic structures (afmI and afmII) and find the afmII structure to be the more stable at low pressures (below 50 GPa), in agreement with previous work. We also find our calculated equations of state for pure iron to be in excellent agreement with previous calculations. Small amounts of nickel (3.5 atm.% and 7 atm.%) were then substituted into each phase to see the effect on the equations of state and the bcc–hcp transition pressure. Our results show that the addition of nickel stabilises the hcp structure with respect to bcc by up to ∼ 20 GPa.