Analysis of thermodynamic properties of fullerite C-60

The thermal expansion coefficients of pure fullerite are determined on the basis of powder x-ray studies in the temperature range 30-293 K. The obtain ed results are in good agreement with dilatometric and neutron-scattering d ata. The data on thermal expansion are used to analyze the heat capacity at constant volume C-V. The intramolecular component of C-V is analyzed consi stently and accurately taking into account the complete set of temperature- dependent intramolecular eigenfrequencies. The rotational component of heat capacity is obtained by subtracting the intramolecular and phonon contribu tions from the total C-V. The phonon component is evaluated on the basis of the Debye model using the Debye temperature (Theta(D)((0))=55.4 K) calcula ted from the known sound velocities. The general and partial Gruneisen para meters are calculated as functions of temperature. The results obtained for the high-temperature phase indicate that rotations of C-60 molecules are s trongly hindered and intercorrelated. (C) 1999 American Institute of Physic s.