Abstract
The present paper deals with the comprehensive studies of phonon dynamics in alkali metal (M) doped C-60 (MC60) solids in fcc phase using a rigid ion model with pairwise interionic interaction potential. The investigations include the computation of the phonon density of states, the specific heat, the Gruneisen parameters, thermal expansion and thermal expansion coefficient and the phonon-dispersion curves of RbC60. The analysis incorporates the van der Waal's and Coulomb interactions for alkali metal-C-60 as well C-60-C-60 molecule and show fairly good agreement with reported inelastic neutron scattering results for RbC60. We have found that thermal expansion coefficient at room temperature is in the range 4.3-6.2 x 10(-5) K-1, which is of the order of pure C-60 solid (6.1 x 10(-5) K-1). Comparing the thermal expansion coefficient of different alkali-doped solids, we conclude that doping decreases anharmonicity in general, and further it decreases with increase in size of the alkali metal. The results have been found to present an overall consistent interpretation of the available experimental data.