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With the aim of producing functional materials based on earth-abundant elements, we examined the synthesis of the ternary type-I clathrates A8AlxSi46−x (A = Na and K). The type-I Si clathrate K7.9(1)Al7.1(1)Si38.9(4), having a lattice parameter of 10.434(1) A, was successfully synthesized via the direct reaction of K, Al, and Si by optimization of both the synthesis temperature and the molar ratios among the raw ingredients. K8Al7Si39 exhibited metallic conduction: its electrical resistivity increased with increasing temperature. The high pressure synthesis of Na8AlxSi46−x was also examined, using a belt-type apparatus and employing a mixture of NaSi, Al, and Si as the reagents. In this manner, the type-I Si clathrate Na8.7(9)Al0.5(1)Si45(2), having a lattice parameter of 10.211(1) A, was synthesized at 5.5 GPa and 1570 K.

Superconducting properties of the polycrystalline Zr2Ru3Si4 were investigated by the electrical resistivity, magnetization and specific heat. By these measurements, bulk superconductivity with transition temperature Tc = 5.5 K was confirmed. Moreover, Zr2Ru3Si4 was found to be a type-II and intermediate-coupling superconductor. Interestingly, the electronic specific heat shows a deviation from a one-gap s-wave model and Hc2(T) shows unusual positive curvature in the vicinity of Tc. The first principle's calculation shows the existence of plural anisotropic Fermi surfaces. These results suggest that Zr2Ru3Si4 is not an isotropic single-gap superconductor, but possibly a multi-gap or an anisotropic gap superconductor., Comment: 13 pages, 6 figures

Measurements of electrical resistivity ρ, magnetization M and specific heat C have revealed that SrPt2Sb2 is a type-II superconducting material with a superconducting critical temperature (Tc) of 2.1 K. The electronic specific heat coefficient γ and the ratio ΔC(Tc)/γTc are 9.2(1) mJ mol−1 K−2 and 1.29, respectively. The temperature dependence of ρ exhibits anomalies around 270 K. Synchrotron x-ray diffraction patterns at 295 and 134 K clearly indicate that SrPt2Sb2 undergoes a structural phase transition in the temperature range from 134 to 295 K, suggesting that the anomalies observed in ρ around 270 K are related to a structural phase transition.