On the Limit of the Thermodynamic Stability of Superheated Crystals and Mechanisms of Its Loss

Abstract

Using the correlative method of unsymmetrized self-consistent field for strongly anharmonic crystals, the thermodynamic stability and the mechanism its loss is studied for crystals with various types of the chemical bond. The following interaction potentials are utilized: the Lennard-Jones pairwise potential together with Axilrod - Teller three-body one for simple van der Waals crystals (solid Ar), effective interionic pairwise potential proposed by Schiff for a metal (Na) and the Girifalco potential for fullerites (C60). In the first and third cases, the FCC lattice becomes unstable because the isothermal bulk modulus BT becomes zero. For fullerites, the shearing coefficient C44 goes to zero as well. Solid Na losses its stability when other shearing coefficient CT11 - CT12 becomes zero.