LOW-TEMPERATURE HEAT-CAPACITY AND LATTICE-DYNAMICS OF C-70

Thermal properties of solid C-70 were investigated by adiabatic calori metry 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 a re estimated. No abnormal behavior and/or relaxation phenomena were ob served even in the phase transition region. Phonon density of states w as calculated on the basis of atom-atom potential method, and it turne d out that the contribution of librational modes was dominant in the l ow frequency region, 10 similar to 20 cm(-1). The calculated heat capa city was in fair agreement with the experimental value in the low temp erature region.