Abstract
Phase transformations in the alkali fulleride RbC 60 between the polymeric, dimeric and metastable fcc phases are investigated by differential scanning calorimetry (DSC) and x-ray diffraction in the ∼215 to 500 K range. The transformation enthalpies of the polymer→monomer and dimer→monomer transitions (25.8 and 10.5 kJ/mol, respectively) are less than expected for covalent interfullerene bonding which suggests substantial contributions from Madelung and deformation energies. Stability of the polymer phase depends on the temperature and duration of polymerization. In samples quenched from 500 to 273 K a transformation from an fcc phase with hindered rotation of the C 60 monomers to another fcc phase in which C 60 − ions are freely rotating is observed at 290 K. The relative Gibbs free energies of the stable and metastable phases are estimated from the measured transformation temperatures and enthalpies. The polymer is the most stable phase at low temperatures.
Published Version
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