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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) Å, c = 22.2845(6) Å] 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 Tc = 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.

Hong Duong Nguyen, Yurii Prots, Walter Schnelle, Bodo Böhme, Michael Baitinger, Silke Paschen, and Yuri Grin, Z. Anorg. Allg. Chem. 2014, 640, (5), 760–767.

Unit cell of Ba3Ge16Ir4 with 26-atom polyhedra (41258,red), 18-atom dodecahedra (4864, blue), and empty 13-atom polyhedra
(4554, light green). Barium atoms are  represented by blue, Iridium atoms by yellow, and germanium atoms by red spheres.
Unit cell of Ba3Ge16Ir4 with 26-atom polyhedra (41258,red), 18-atom dodecahedra (4864, blue), and empty 13-atom polyhedra (4554, light green). Barium atoms are represented by blue, Iridium atoms by yellow, and germanium atoms by red spheres.
Electron localizability indicator Y (ELI-D) in Ba3Ge16Ir4. Two top panels show ELI-D distribution at x = 0, middle left panel illustrates the section at z = 0.5, two other maps reveal ELI-D distribution in the planes crossing Ir1 and Ge4 (middle right panel) and Ge1 and Ge4 (bottom panel) atoms, respectively.
Electron localizability indicator Y (ELI-D) in Ba3Ge16Ir4. Two top panels show ELI-D distribution at x = 0, middle left panel illustrates the section at z = 0.5, two other maps reveal ELI-D distribution in the planes crossing Ir1 and Ge4 (middle right panel) and Ge1 and Ge4 (bottom panel) atoms, respectively.