Low temperature heat capacity and lattice dynamics of C-70

Thermal properties of solid C-70 were investigated by adiabatic calorimetry and DTA between 5 and 370 K. The heat capacity anomalies caused by the orientational phase transitions were observed at about 280 and 340 K. The thermodynamic quantities related to the phase transitions are estimated. No abnormal behavior and/or relaxation phenomena were observed even in the phase transition region. Phonon density of states was calculated on the basis of atom-atom potential method, and it turned out that the contribution of librational modes was dominant in the low frequency region, 10 similar to 20 cm(-1). The calculated heat capacity was in fair agreement with the experimental value in the low temperature region.