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

TL;DR

This paper investigates the limits of thermodynamic stability in superheated crystals with various bonding types using advanced self-consistent field methods, revealing specific instability mechanisms and critical points for different materials.

Contribution

It introduces a correlative method for analyzing anharmonic crystals and identifies the specific conditions leading to stability loss in different crystal types.

Findings

FCC lattice becomes unstable when bulk modulus BT reaches zero.

Fullerites lose stability as shearing coefficient C44 approaches zero.

Solid Na destabilizes when shearing coefficient CT11 - CT12 becomes zero.

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.