B.c.c. and h.c.p. phase competition in Fe

¹ Institut Romand de Recherche Numérique en Physique des Matériaux PHB-Ecublens, CH-1015 Lausanne, Switzerland
² Département de Physique de la Matière Condensée, Université de Genève CH-1211 Genève, Switzerland

Received: 23 August 1995
Accepted: 4 December 1995

Abstract

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 methods. The electronic and pV contributions to Gibbs energy show a non-linear 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 entropy 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.