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) Aa, c = 22.2845(6) Aa] was refined from single-crystal X-ray diffraction data. The phase was obtained after 10 d at 910 C with small impurities of clathrate-I, BaGe₇Ir₂ and α-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. (Copyright copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)