Heat capacity of a giant single crystal of C 60

Abstract

The heat capacity of a giant single crystal of C 60 (8×6×6 mm 3) was measured from 6 to 350 K by adiabatic calorimetry. A very sharp first-order phase transition arising from the orientational ordering of C 60 molecules was observed at 262.1 K, and a glass transition due to freezing of the reorientational motion of C 60 molecules was also found at 84.6 K. The transition temperature and the height of the heat capacity peak are much higher than any other calorimetric results reported previously. The transition enthalpy and entropy are also large in comparison with the values determined hitherto for a powder sample. These facts reveal that the phase transition of C 60 is strongly affected by crystallinity as well as purity. The C 60 giant single crystal used here is supposed to be free from these effects. The present results may be considered as reference thermodynamic values and behavior for crystalline C 60.