Rotational dynamics of C-60 in superconducting K3Ba3C60

The orientational dynamics of C-(x) in superconducting K3Ba3C60 are studied by neutron inelastic scattering. Low-energy excitations are present near s imilar to 6 meV between 150 and 320 K and are assigned to small-amplitude l ibrations of the C-60(9-) ions. They are harder and broader than those meas ured in K3C60. reflecting the existence of a stronger and more anisotropic orientational potential. The anisotropy and dispersion effects are also lar ger than those in isostructural Rb6C60, as. a result of positional disorder of the Ba2+ and K+ ions. which reside in distorted tetrahedral interstices . The estimated barrier of the hindrance potential, E-a, is similar to 1.4 eV. (C) 2000 Elsevier Science B.V. All rights reserved.