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 divacancies. 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. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA

Thermal vacancy effects on the thermodynamic properties and stability of fullerites

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 C60 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. © 2005 American Chemical Society

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 divacancies. 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. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA

Thermal vacancy effects on the thermodynamic properties and stability of fullerites

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 C60 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. © 2005 American Chemical Society

Molecular interactions in fullerenes and equilibrium of higher fullerites C76 and C84 with their vapors

From simple topological considerations on the molecular shapes, a new method for calculating the coefficients of the Girifalco intermolecular potential for various fullerenes is proposed. This eliminates the necessity for fitting the coefficients to data of measurements for each specific fullerene. We calculate them for C76 and C84 and apply this potential to perform research on the equilibrium of these fullerites with their vapors. The temperature dependence of the lattice parameters, the saturated vapor pressures and the enthalpies of sublimation is studied. Results are in good agreement with available experimental data

Statistical mechanical study of thermodynamic properties of a family of fullerites from C36 to C96 in the equilibrium with their vapors

The temperature dependence of saturated vapor pressure of fullerites C36-C96 and their thermodynamic properties along with the sublimation curves up to the spinodal are calculated. The saturated vapor pressures along all the range of temperatures are approximated by logPsat = A - (B/T) - CT. The coefficient A practically does not depend on the number of atoms in the molecule (varying only by 2.2%), B increases noticeably while C decreases from the C36 to the C96, both of them by approximately two. The isothermal bulk modulus BT and the shear modulus C44 vanish at the spinodal points. © 2004 Taylor & Francis Group, LLC

Theoretical study of thermodynamic properties of a family of fullerites from C-36 to C-96 in the equilibrium with their vapors

On the basis of the correlative method of the unsymmetrized self-consistent field that yields the account of the strong anharmonicity of the lattice vibrations, it has been calculated the temperature dependence of saturated vapor pressure of higher and smaller fullerites, from C-36 up to C-96, and their thermodynamic properties along their sublimation curves. We have used the intermolecular potential of Girifalco with parameters recently calculated for these fullerenes. The calculations were accomplished up to the temperature of loss of stability (spinodal point) T-s. We compare our results with available experimental data and with quantities calculated earlier for the magnitudes of the most widespread of the fullerites, the C-60. The behavior of some characteristics is considered in their dependence on the number of atoms in the molecule. The saturated vapor pressures up to the spinodal points of the two-phase systems crystal-gas is approximated by the formula log P-sat = A - (B/T) - CT, where the last term is related to the anharmonicity of the lattice vibrations. The coefficient A practically has no dependence on the number of atoms in the molecule (varying only by 2.2%); B increases monotonically, while C decreases from C-36 to C-96 by approximately twice. The isothermal bulk modulus B-T and the shear modulus C-44 vanish at the spinodal points

Statistical mechanical study of thermodynamic properties of a family of fullerites from C36 to C96 in the equilibrium with their vapors

The temperature dependence of saturated vapor pressure of fullerites C36-C96 and their thermodynamic properties along with the sublimation curves up to the spinodal are calculated. The saturated vapor pressures along all the range of temperatures are approximated by logPsat = A - (B/T) - CT. The coefficient A practically does not depend on the number of atoms in the molecule (varying only by 2.2%), B increases noticeably while C decreases from the C36 to the C96, both of them by approximately two. The isothermal bulk modulus BT and the shear modulus C44 vanish at the spinodal points. © 2004 Taylor & Francis Group, LLC

Theoretical Study of Thermodynamic Properties of a Family of Fullerites from C36 to C96 in the Equilibrium with Their Vapors

On the basis of the correlative method of the unsymmetrized self-consistent field that yields the account of the strong anharmonicity of the lattice vibrations, it has been calculated the temperature dependence of saturated vapor pressure of higher and smaller fullerites, from C36 up to C96, and their thermodynamic properties along their sublimation curves. We have used the intermolecular potential of Girifalco with parameters recently calculated for these fullerenes. The calculations were accomplished up to the temperature of loss of stability (spinodal point) T s. We compare our results with available experimental data and with quantities calculated earlier for the magnitudes of the most widespread of the fullerites, the C60. The behavior of some characteristics is considered in their dependence on the number of atoms in the molecule. The saturated vapor pressures up to the spinodal points of the two-phase systems crystal-gas is approximated by the formula log Psat = A (BIT) - CT, where the last term is related to the anharmonicity of the lattice vibrations. The coefficient A practically has no dependence on the number of atoms in the molecule (varying only by 2.2%); B increases monotonically, while C decreases from C36 to C96 by approximately twice. The isothermal bulk modulus BT and the shear modulus C44 vanish at the spinodal points

Theoretical study of thermodynamic properties of a family of fullerites from C-36 to C-96 in the equilibrium with their vapors

On the basis of the correlative method of the unsymmetrized self-consistent field that yields the account of the strong anharmonicity of the lattice vibrations, it has been calculated the temperature dependence of saturated vapor pressure of higher and smaller fullerites, from C-36 up to C-96, and their thermodynamic properties along their sublimation curves. We have used the intermolecular potential of Girifalco with parameters recently calculated for these fullerenes. The calculations were accomplished up to the temperature of loss of stability (spinodal point) T-s. We compare our results with available experimental data and with quantities calculated earlier for the magnitudes of the most widespread of the fullerites, the C-60. The behavior of some characteristics is considered in their dependence on the number of atoms in the molecule. The saturated vapor pressures up to the spinodal points of the two-phase systems crystal-gas is approximated by the formula log P-sat = A - (B/T) - CT, where the last term is related to the anharmonicity of the lattice vibrations. The coefficient A practically has no dependence on the number of atoms in the molecule (varying only by 2.2%); B increases monotonically, while C decreases from C-36 to C-96 by approximately twice. The isothermal bulk modulus B-T and the shear modulus C-44 vanish at the spinodal points