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Abstract: 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 determined by magnetization measurements, the penetration depth and the coherence length are estimated for Ba8Si46. The high density of states at the Fermi level is the most important parameter to give rise to a relatively high in Ba8Si46, while the high phonon frequency is essential for K3C60. In contrast, the experimental facts found in where and Ge imply that the rattling phonons in the open cage potentials seem to control the superconducting transition temperature. [Copyright &y& Elsevier]

Abstract: Physical properties of a new superconductor Ba24Si100 crystallographically identical to Ba24Ge100 are studied by electric transport, specific heat capacity and magnetic susceptibility measurements. The density of states at the Fermi level N EF=0.148 stateseV−1 (Si-atom)−1 and a discrete jump of C p at the superconducting transition temperature ΔC p=0.272JK−1 mol−1 are obtained. The exponential fit of C p under the superconducting states gives an energy gap 2Δ=0.423meV and shows that this is a superconductor having an s-wave character or an isotropic energy gap. On the basis of the experimental data, other important physical parameters are also described. [Copyright &y& Elsevier]

Abstract: A Si136 compound with an endohedral accommodation of Ba is newly made and its electronic states are compared to those of pure silicon-network superconducting Ba8Si46. The resulting Na16Ba8Si136 has indeed a small density of states at the Fermi level and does not superconduct down to 2 K. Rietveld analyses show that Ba is accommodated in a Si28 cage with 0.98 occupancy and Na in Si20 with 0.61. The disappearance of superconductivity could be explained in terms of the little hybridization of Ba 5d/6s with Si28 polyhedral cluster orbitals, leading to a very low density of states at the Fermi level. [Copyright &y& Elsevier]

Abstract: The solid solutions BaAl1−x Si1+x (0⩽ x ⩽0.5) were prepared. The compound with the stoichiometric composition (x =0) did not show superconductivity as reported by other investigators, but the solid solutions with x >0 became superconductors with a transition temperature T c =2.8K. The comparison of the lattice parameters with those of the other isotypic ternary superconductors MAlSi (M=Ca,Sr) suggested that the superconductivity could be related to the lattice parameter within the (AlSi) plane rather than the interlayer spacing. The band structures near the Fermi level of MAlSi (M=Ca,Sr,Ba) were measured using soft X-ray photoelectron spectroscopy, which were in good agreement with the calculated ones, confirming that the contribution of the d orbitals of the alkaline-earth metals were predominant in the conduction bands. [Copyright &y& Elsevier]