BCC AND HCP PHASE COMPETITION IN FE

The electronic and vibrational free energies of the b.c.c., f.c.c. and h.c.p. phases of iron are calculated by ab initio band structure meth ods. The electronic and pV contributions to Gibbs energy show a non-li near dependence with temperature and play an important role for the h. c.p.-b.c.c. phase stability. The b.c.c. phase is found to be stable at low pressure. For large pressure, an upper limit of the magnetic entr opy is estimated. It lowers Gibbs energy of the b.c.c. phase, but with all energy terms, h.c.p. included, remains stable at all temperatures .