Thermodynamics of crystalline dimer of fullerene C60 in the range from T→0 to 340 K at standard pressure

By adiabatic vacuum calorimetry the temperature dependence of heat capacity for crystalline dimer of fullerene C-60 has been determined in the range 6-340 K at standard pressure. Between 46 and 56 K, a glass-like transition of the dimer, the nature of which is, probably, similar to that described for C60, has been found. The results were used to calculate the thermodynamic functions of the dimer: the heat capacity C(p)degrees(T), enthalpy Hdegrees(T) - Hdegrees(0), entropy Sdegrees(T) - Sdegrees(0) and Gibbs function Gdegrees (T) - Hdegrees (0) over the range from T --> 0 P to 340 K. For T < 60 K the fractal dimension D in the heat capacity function of the multifractal variant of the Debye's theory of heat capacity was estimated and in the 20-45 K range D was found to be 1. That indicates a chain structure of the dimer. The heat capacities of the dimer have been compared to those of the initial fullerite C-60. The standard entropy of formation of the crystalline dimer from graphite, at T = 298.15 K and at standard pressure, and the entropies of transition of the initial fullerite C-60 to the crystalline dimer have been calculated. (C) 2002 Elsevier Science B.V. All rights reserved.