Sp³-network superconductors made from IVth-group elements

Discussions are made among the polyhedral superconductors made from IVth-group elements (C, Si and Ge). Important superconducting physical parameters of Ba8Si46 are deduced from magnetic measurements and are compared to those of K3C60. Using the lower and the upper critical fields of 78 and 5.5 ×104 Oe determined by magnetization measurements, the penetration depth λ= 270 nm and the coherence length ξ= 7.7 nm are estimated for Ba8Si46. The high density of states at the Fermi level isthe most important parameter to give rise to a relatively high Tc in Ba8Si46, while the high phonon frequency is essential for K3C60. In contrast, the experimental facts foundin IV100 where IV = Si and Ge imply that the rattling phonons in the open cage potentials seem to control the superconducting transition temperature.