Thermodynamics of crystalline dimer of fullerene C 60 in the range from T → 0 to 340 K at standard pressure

Abstract

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 C 60, has been found. The results were used to calculate the thermodynamic functions of the dimer: the heat capacity C p ∘( T), enthalpy H °( T)− H °(0), entropy S °( T)− S °(0) and Gibbs function G °( T)− H °(0) over the range from T→0 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.