THERMODYNAMIC CHARACTERIZATION OF C-60 BY DIFFERENTIAL SCANNING CALORIMETRY

Heat capacity measurements on C60 were carried out by differential scanning calorimetry from 120 to 560 K. This heat capacity was linked based on existing normal-mode and lattice calculation, to the vibrational heat capacities. In this way the thermodynamic functions are available from absolute zero of temperature. The phase transition at 256 K could be identified as a crystal-to-plastic crystal transition with an increase in entropy of 27.3 J/(K mol). A broad beginning of this transition at 190 K is linked to the change from a jumplike rotation that is starting already at about 100 K without increase in entropy to the rotational motion that ultimately causes the disordering transition. This classification is based on reinterpretation of the solid-state NMR results with calorimetry data. No melting temperature could be detected up to 950 K, the temperature limit of our calorimeter.