Fizika Nizkikh Temperatur: Volume 25, Number 8-9 (August 1999), p. 964-975 ( to contents , go back )
Analysis of thermodynamic properties of fullerite C60
N. A. Aksenova, A. P. Isakina, A. I. Prokhvatilov, and M. A. Strzhemechny
B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47, Lenin Ave., 310164, Kharkov, Ukraine
(Received March 2, 1999, revised April 21, 1999 )
The powder x-ray studies were performed to determine thermal expansion coefficients and molar volumes of pure fullerite C60 over the temperature range 30-293 K. The data are in good agreement with dilatometric and neutron-scattering data. The data on thermal expansion are used to analyze the constant-volume heat capacity. The heat capacity due to intramolecular modes is consistently and accurately calculated. The rotational heat capacity is obtained by subtracting the intramolecular and phonon contributions from the total CV. The phonon contribution is evaluated using the Debye model (QD(0)) calculated from the known sound velocities. The general and partial Gruneisen parameters are calculated as a function of temperature. The results obtained give evidence that the rotations of C60 molecules in the high-temperature phase are strongly hindered and intercorrelated.