We have measured the low-energy neutron inelastic-scattering (NIS) spectra of superconducting Na2RbC60 in the temperature range 50--350 K. Well-defined librational peaks are observed at 50 K at 2.83(17) meV (FWHM = 1.7(5) meV). They soften and broaden with increasing temperature. Their behaviour mimics that found in solid C60 and differs markedly from K3C60. The rotational barrier for C60 reorientations in Na2RbC60 is somewhat higher than in pristine C60 and approximately half as large as in K3C60. An order-disorder transition is anticipated at a temperature higher than that found in C60.
ASJC Scopus subject areas
- Physics and Astronomy(all)