Melting as a first‐order phase transition in a system of defects

Abstract

AbstractThe self‐consistent quasiharmonic model is used to describe the equilibrium atomic structure of a crystal and the thermodynamical properties of vacancies at high temperature. It is shown that an increase in the amplitude of the thermal atomic vibrations with temperature leads to a considerable reduction of the vacancy formation energy in the high‐temperature region, which results in the generation of a large number of defects near the melting point and, as a consequence, in the significant softening of the acoustic vibration modes of the crystal. The effective attraction between the vacancies through the phonon subsystem of the crystal is found to lead to the first‐order phase transition with a discontinuous change in the defect concentration at the transition point. The melting lines are calculated for the rare gas crystals. The effects of the solid–vapour interface on the kinetics of the solid‐liquid transition are studied.