Synthesis and structure of type -II clathrates Cs8Na16Ga6Ge130, Cs8Na16Si22.0(3)Ge114.0(3) and Rb8Na16Si13.7(4)Ge122.3(4)

The type-II clathrates of Cs8Na16Ga6Ge130, Cs8Na16Si22.0(3)Ge114.0(3) and Rb8Na16Si13.7(4)Ge122.3(4) have been synthesized from elements. The structures were refined from the powder X-ray diffraction data using the WinCSD program. Cs8Na16Ga6Ge130, Cs8Na16Si22.0(3)Ge114.0(3) and Rb8Na16Si13.7(4)Ge122.3(4) crystallized in the space group Fd3m with the lattice parameters of a = 15.48499 (3) angstrom, 15.44642(6) angstrom and 15.47489(5) angstrom, respectively. The theoretical calculation indicates the metallic features for Cs8Na16Ga6Ge130, Cs8Na16Si22.0(3)Ge114.0(3) and Rb8Na16Si13.7(4)Ge122.3(4. The heat capacity measurement shows a large electron contribution and a strong Einstein mode in Cs8Na16Ga6Ge130. The magnetic measurement evidences a diamagnetic behaviour for Cs8Na16Si22.0(3)Ge114.0(3) in the temperature range of 1.8-300 K.