Superconductivity in the(Ba1−xSrx)8Si46<

Abstract

Si clathrates ͑Ba 1−x Sr x ͒ 8 Si 46 with x ഛ 0.75 have been successfully synthesized and their superconductivity studied both experimentally and by ab initio calculations. The linear decrease of the cubic lattice parameter with the Sr content shows the continuous shrinkage of the constituting ͑Ba/ Sr͒ @ Si20 and ͑Ba/ Sr͒ @ Si24 cages, while the critical superconducting transition temperature T c decreases from 8 K to 4.1 K at 75% of substitution. The experimentally extrapolated value for the T c of the hypothetical Sr 8 Si 46 is in good agreement with the calculated one of 3 K. The lower contribution of the Sr d-electrons to the density of states at the Fermi energy explains the observations.

Cagelike Diamondoid Nitrogen at High Pressures

“…Besides the known B-cage in α-boron or γ-boron [35], C-cages in C 60 or C 70 [36], and Si/Ge-cages in clathrates (e.g., in Ba 8 Si 46 [37]), we have also found a H-cage in a hydrogen sodalite structure in CaH 6 [38]. C has the right number of electrons and forms conjugated π bonds.…”

Lattice stability of intermediate phases of the Sr–Si system

“…In addition CaSi 2 and BaSi 2 and several Ga or Al doped ternary alkalineearth metal (AEM, i.e. Ca, Sr and Ba) silicides show interesting superconducting properties at low temperatures [7][8][9] as well as some Ba-or Sr-based Si and Ge clathrates [10,11]. These interesting physical properties arise from the peculiar AEM-Si chemical bond in the solid state that is qualitatively predicted to be mainly ionic.…”

Energetic evaluation of Ba– and Sr–Si clathrate formation at high pressures by first-principle pseudopotential calculations

“…Because the relatively high superconducting temperature (T c ) is related to the high Debye frequency in accordance with the conventional phonon-mediated BCS mechanism, Toulemonde et al [2] have performed a series of experiments to synthesize the silicon clathrate (Ba 1Àx Sr x ) 8 Si 46 using a high-pressure-high-temperature (HPHT) technique. It was expected that the shorter Si-Si distance brought about by incorporation of Sr into Ba 8 Si 46 would result in higher phonon-electron coupling and higher Tc 1 .…”