Polymorphism in Metals I. Vibrational Free Energy

Abstract

At least 26 metals transform at ordinary pressure from a low temperature close-packed structure to a high temperature bcc phase. According to an old hypothesis of Zener, this is caused by a somewhat lower Debye temperature in a bcc lattice. This idea is investigated in detail and confirmed both by theoretical calculations and analysis of experimental data. Most polymorphic transformations occur quite close to the melting temperature but even so, anharmonicity does not cause the change in crystal structure.