Yb9+xCuMg4–x (x = 0.034): A κ-Phase Formed by Lanthanoids

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• 作者：Serena De Negri ; Vitaliy Romaka ; Pavlo Solokha ; Adriana Saccone ; Gerald Giester ; Herwig Michor ; Peter F. Rogl
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：August 15, 2016
• 年：2016
• 卷：55
• 期：16
• 页码：8174-8183
• 全文大小：849K
• 年卷期：0
• ISSN：1520-510X

文摘

Atom order in the crystal structures of Yb₂Cu_2–xMg (x = 0.17; Mo₂FeB₂-type; P4/mbm; a = 0.75592(2) nm; c = 0.40282(1) nm) and Yb_9+xCuMg_4–x (x = 0.034; Hf₉Mo₄B-type; P6₃/mmc; a = 1.0169(5) nm; c = 1.0290(5) nm) was determined from powder and X-ray single-crystal counter data analyses supported by electron probe microanalyses. Among the group of the so-called κ-phases, Yb_9+xCuMg_4–x is the first representative formed by a lanthanoid element. The structure of this κ-phase can be viewed as a typical network of corner-connected empty Yb₆-octahedra, which encompass Yb₆Mg₆-icosahedra (filled by a mix of Mg/Yb atoms) and Yb₆-trigonal prisms centered by Cu atoms to complete the three-dimensional metal framework. From another point of view, the same structure is considered as built from infinite polyicosahedral columns of Yb₉Mg₄ composition with Cu atoms located in trigonal prismatic interstices, highlighting similarities with other Yb-rich Yb–Cu–Mg phases. Density functional theory (DFT) calculations classify Yb₉CuMg₄ as a polar intermetallic. Metallic-like behavior is inferred from the Sommerfeld constant, γ = 49.2 mJ/mol·K², derived from the electronic density of states, calculated at the Fermi level. DFT integration of the f-density of states indicates almost completely filled f-states, revealing 13.6 and 13.7 electrons in the valence band for Yb1 and Yb2 atoms, respectively, close to the Yb²⁺ ground state (¹S₀) for both Yb atoms. Magnetic susceptibility data recorded on the same compound are consistent with a nonmagnetic divalent Yb²⁺ state. Temperature-dependent heat capacity data display a metallic behavior characterized by a small Sommerfeld constant γ = 64.8 mJ/mol·K² and a rather low Debye temperature Θ_D = 140 K as typical for soft materials.