Preparation, Crystal Structure and Physical Properties of the Superconducting Cage Compound Ba3Ge16Ir4

The cage compound Ba3Ge16Ir4 crystallizes with the Ba3Ge16Rh4 type of crystal structure, which represents a hierarchical derivative of the BaAl4 type. The crystal structure [Pearson symbol tI46, space group I4/mmm; a = 6.5312(2) angstrom, c = 22.2845(6) angstrom] was refined from single-crystal X-ray diffraction data. The phase was obtained after 10 d at 910 degrees C with small impurities of clathrate-I, BaGe7Ir2 and -Ge remaining at the grain boundaries. Ba3Ge16Ir4 is a Pauli-paramagnetic metal, which becomes superconducting below T-c = 5.1 K. Electronic structure and analysis of the chemical bonding were performed based on density functional theory calculations. The physical properties are discussed in comparison to the isotypic phase Ba3Ge16Rh4.