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 sp³ bonds between C₆₀ molecules. Specific heat is then measured over the temperature range of 300--2K. 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.