Migration enthalpies in FCC and BCC metals

Abstract

The authors present a model relating the migration enthalpy Hvm for nearest-neighbour vacancy jumps in cubic metals to the phonon dispersion. The migration enthalpy is split into two parts, one depending only on the lattice structure, the other on the vibrational properties of the particular metal. This latter term can be written in terms of the static lattice Green function, i.e. of the omega -2 moment of the spectrum. It can thus be calculated directly from measured phonon dispersion curves. For FCC metals, excellent agreement between calculated and measured values of Hvm is found. For BCC metals, where Hvm is known from experiments only in a few cases, predictions are made wherever the phonon dispersions are available. The model takes into account the unusually low-lying phonon branches in some of the BCC metals and yields, where phonon frequencies shift with temperature, temperature-dependent values of Hvm.