Thermodynamic properties of some polymeric forms of fullerite C-60 at temperatures ranging from 0 to 320 K

The temperature dependences of the heat capacity C(p)degrees of fullerites C-60 were studied at temperatures ranging from 5 to 320 K in an adiabatic v acuum calorimeter with an accuracy of 0.4-0.2%. The fullerite C-60 samples were prepared by treating the starting fullerite C-60 under 8 GPa at 920 an d 1270 K and "quenched" by a sharp decrease in pressure to similar to 10(5) Pa and in temperature to similar to 300 K. Fullerite C-60(8 GPa, 920 K), a crystalline polymer with layered structure formed by polymerized fullerene C-60 molecules, was obtained at 920 K and 8 GPa. Fullerite C-60(8 GPa, 127 0 K), a three-dimensional polymer with a graphite-like structure formed by fragments of decomposed C-60 molecules and containing many C(sp(3))-C(sp(3) ) bonds, was obtained at 1270 K and 8 GPa. Both polymers are metastable pol ymeric phases. The anomalous character of the temperature dependence of the heat capacity was revealed in the 49-66 K range for the polymer formed at 1270 K. The thermodynamic functions of the substances under study were calc ulated for the 0-320 K region along with entropies of their formation from graphite. The entropies of transformation of the starting fullerite C-60 in to metastable phases and that of intertransformation of phases were estimat ed.