Superconductivity in silicon based barium-inclusion clathrates

Clathrates of type Ba8TMxSi46−x (with TM = Au, Ag, Cu) have been investigated. We report on superconductivity in Ba-inclusion silicon based clathrates when doped with transition metals. It is clarified that the transition metals are necessary in order to form the clathrates as major phases, but they destroy the superconductivity. On lowering the amount of TM, an increase in superconducting fraction has been observed, with a maximum at x≈1. After purification a superconducting fraction of up to 50% was obtained. The critical temperatures range from 5 to 6 K depending on both, x and the type of TM.