Specific Heat of Rhombohedral Polymeric C60 in Temperature Range 300--2K

Polymerization of C60 is realized under high temperature and high pressure. X-ray diffraction reveals a rhombohedral lattice structure in the product, and solid-state ^13C nuclear magnetic resonance spectroscopy confirms the formation of sp^3 bonds between C60 molecules. Specific heat is then measured over the temperature range of 300-2 K. It is found that its specific heat values are significantly less than those in fullerite within the region of 80-2K, and this huge reduction is attributed to the suppression of intermolecular librational modes in polymerized C60. An excellent fit to the experimental data over the entire temperature range is provided by a model, which needs to include only three-dimensional and two-dimensional translational modes in various contributions at different temperatures.