On the thermal vacancy effects on thermodynamic properties and stability of Van der Waals crystals

Reverting to an investigation of thermal vacancies in simple Van der Waals crystals [phys. stat. sol. (b) 101, 95 (1980)] we take into account the possibility of forming their bonded complexes, in particular di-vacancies. We use the correlative method of the unsymmetrized self-consistent field (CUSF) that enables one to include the strong anharmonicity of the lattice vibrations. We have calculated the parameters of the vacancy formation, the vacancy and divacancy concentration in solid Ar and contribution of the defects to its equilibrium thermodynamic properties, depending on the temperature and pressure, such contributions to components of the elastic tensor are studied for the first time. We also investigate the influence of defects on the thermodynamic stability of crystal lattice.