Thermal Vacancy Effects on the Thermodynamic Properties and Stability of Fullerites

Abstract

We study the influence of thermal vacancies on equilibrium thermodynamic properties of the high-temperature phase of fullerites taking into account the strong anharmonicity of the lattice vibrations. Treating a crystal with point defects as a quasi-multicomponent system and using the correlative method of the unsymmetrized self-consistent field and the Girifalco interaction potential for the molecular subsystem, we have obtained the vacancy formation parameters for the C(60) fullerite. We also take into account the divacancies. The influence of the lattice defects on the specific heats of fullerites is negligible, since a dominant contribution to them is given by intramolecular degrees of freedom. We have calculated the contributions of vacancies to various thermodynamic properties, the volume thermal expansion coefficient, the isothermal bulk modulus, and the components of the isothermal elastic tensor, depending on the temperature and pressure. Near the estimated triple point, these contributions run to more than 10% and increase still further at a metastable region. We also discuss the influence of defects on the thermodynamic stability of fullerites.

Structure formation processes in fullerene mixtures

“…The interaction between the molecules is determined by the effective short-range potential of the intermolecular interaction of the spherical typethe Girifalco potential [15][16][17][18].…”

Процессы Структурообразования В Фуллереновых Смесях

“…Рассматривается система состоящая из 32 000 молекул (6400 и 25 600 молекул фуллеренов C 60 и C 70 соответственно), расположенных в кубической ячейке с периодическими граничными условиями. Взаимодействие между молекулами задается с помощью эффективного короткодействующего потенциала межмолекулярного взаимодействия сферического типа -потенциала Жирифалько [15][16][17][18]. Физические величины измеряются в параметрах потенциала как представлено в работе [19].…”