Lattice dynamics of RbC60 in its rotator, polymer, and dimer phase: A neutron-scattering investigation.

Abstract

Investigations of Rb${\mathrm{C}}_{60}$ give evidence for characteristic differences in the spectra of low-energy lattice vibrations between the high-temperature dynamically disordered and the low-temperature ordered polymer and dimer phases. These changes are consistent with a formation of inter-${\mathrm{C}}_{60}$ covalent bonds. A softening of lattice modes is observed as a precursor of the 390-K order and/or disorder transition. Evidence is obtained for an anomalous low-temperature behavior of low-energy modes in the polymer phase, but a connection with the proposed metal-to-insulator transition at 50 K cannot be established.