Rhombohedrally Distorted 纬-Au5鈥?i>xZn8+y Phases in the Au鈥揨n System

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• 作者：Srinivasa Thimmaiah ; Gordon J. Miller
• 刊名：Inorganic Chemistry
• 出版年：2013
• 出版时间：February 4, 2013
• 年：2013
• 卷：52
• 期：3
• 页码：1328-1337
• 全文大小：502K
• 年卷期：v.52,no.3(February 4, 2013)
• ISSN：1520-510X

文摘

The region of the Au鈥揨n phase diagram encompassing 纬-brass-type phases has been studied experimentally from 45 to 85 atom % Zn. The 纬 phases were obtained directly from the pure elements by heating to 680 掳C in evacuated silica tubes, followed by annealing at 300 掳C. Powder X-ray and single-crystal diffraction studies show that 纬-鈥淎u₅Zn₈鈥?phases adopt a rhombohedrally distorted Cr₅Al₈ structure type rather than the cubic Cu₅Zn₈ type. The refined compositions from two single crystals extracted from the Zn- and Au-rich loadings are Au_4.27(3)Zn_8.26(3)鈻?sub>0.47 (I) and Au_4.58(3)Zn_8.12(3)鈻?sub>0.3 (II), respectively (鈻?= vacancy). These (I and II) refinements indicated both nonstatistical mixing of Au and Zn atoms as well as partially ordered vacancy distributions. The structures of these 纬 phases were solved in the acentric space group R3m (No. 160, Z = 6), and the observed lattice parameters from powder patterns were found to be a = 13.1029(6) and 13.1345(8) 脜 and c = 8.0410(4) and 8.1103(6) 脜 for crystals I and II, respectively. According to single-crystal refinements, the vacancies were found on the outer tetrahedron (OT) and octahedron (OH) of the 26-atom cluster. Single-crystal structural refinement clearly showed that the vacancy content per unit cell increases with increasing Zn, or valence-electron concentration. Electronic structure calculations, using the tight-binding linear muffin-tin orbital method with the atomic-sphere approximation (TB-LMTO-ASA) method, indicated the presence of a well-pronounced pseudogap at the Fermi level for 鈥淎u₅Zn₈鈥?as the representative composition, an outcome that is consistent with the Hume鈥揜othery interpretation of 纬 brass.