Calorimetric study of crystalline dimer and polymerized phases of fullerene C60

By high precision dynamic calorimetry the temperature dependences of heat capacity Cp0=f(T) for dimer of C60, orthorhombic and rhombohedral polymerized phases of fullerene C60 were determined in the temperature range 300–650 K. Besides, endothermic transformations caused by the depolymerization of the polymerized (dimeric) phases of C60 were studied and their standard thermodynamic characteristics a temperature interval, enthalpy, entropy and Gibbs function were analyzed. Based on the thermodynamic and oscillation spectroscopy data, it was established that the depolymerization proceeds completely and the products formed are a monomer fcc phase of C60. From the data of the present work and the heat capacity values measured by us earlier in a low-temperature interval, the thermodynamic functions of the substances, viz. the heat capacity Cp0(T), enthalpyH0(T)−H0(0), entropy S0(T)−S0(0) and Gibbs function G0(T)−H0(0), were calculated over the range from T→0 to (380–490) K at standard pressure. The results were discussed taking into account literature data. A sequence of a relative thermodynamic stability at 298.15 K and atmosphere pressure of the crystalline polymerized C60 phases was arranged.