Calorimetric study of crystalline dimer and polymerized phases of fullerene C 60

Abstract

By high precision dynamic calorimetry the temperature dependences of heat capacity C p 0= f( T) for dimer of C 60, orthorhombic and rhombohedral polymerized phases of fullerene C 60 were determined in the temperature range 300–650 K. Besides, endothermic transformations caused by the depolymerization of the polymerized (dimeric) phases of C 60 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 C 60. 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 C p 0( T), enthalpy H 0( T)− H 0(0), entropy S 0( T)− S 0(0) and Gibbs function G 0( T)− H 0(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 C 60 phases was arranged.