Vibrational properties and superconductivity in Ba 24 Si 100

The vibrational spectrum for the type-III Si-clathrate Ba24Si100 has been computed from first principles electronic structure method. It is shown that the Ba vibrations are strongly hybridized with the host lattice in the cages formed by coordinately unsaturated Si. The electron-phonon coupling spectral function calculated from zone center phonons indicates that electron-phonon interaction is stronger for low-frequency Ba vibrations in the loosely enclathrated cages than those in the more tightly fitted cages. A similar trend was also observed in the related Ba8Si46 and Ba6Na2Si46 systems. The results show that low-frequency rattling vibrations of the Ba atoms are very efficient in mediating electron-phonon coupling in the superconductivity behaviour of these novel materials.