Clathrate Ba8Au16P30: The 鈥淕old Standard鈥?for Lattice Thermal Conductivity

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• 作者：James Fulmer ; Oleg I. Lebedev ; Vladimir V. Roddatis ; Derrick C. Kaseman ; Sabyasachi Sen ; Juli-Anna Dolyniuk ; Kathleen Lee ; Andrei V. Olenev ; Kirill Kovnir
• 刊名：The Journal of the American Chemical Society
• 出版年：2013
• 出版时间：August 21, 2013
• 年：2013
• 卷：135
• 期：33
• 页码：12313-12323
• 全文大小：780K
• 年卷期：v.135,no.33(August 21, 2013)
• ISSN：1520-5126

文摘

A novel clathrate phase, Ba₈Au₁₆P₃₀, was synthesized from its elements. High-resolution powder X-ray diffraction and transmission electron microscopy were used to establish the crystal structure of the new compound. Ba₈Au₁₆P₃₀ crystallizes in an orthorhombic superstructure of clathrate-I featuring a complete separation of gold and phosphorus atoms over different crystallographic positions, similar to the Cu-containing analogue, Ba₈Cu₁₆P₃₀. Barium cations are trapped inside the large polyhedral cages of the gold鈥損hosphorus tetrahedral framework. X-ray diffraction indicated that one out of 15 crystallographically independent phosphorus atoms appears to be three-coordinate. Probing the local structure and chemical bonding of phosphorus atoms with ³¹P solid-state NMR spectroscopy confirmed the three-coordinate nature of one of the phosphorus atomic positions. High-resolution high-angle annular dark-field scanning transmission electron microscopy indicated that the clathrate Ba₈Au₁₆P₃₀ is well-ordered on the atomic scale, although numerous twinning and intergrowth defects as well as antiphase boundaries were detected. The presence of such defects results in the pseudo-body-centered-cubic diffraction patterns observed in single-crystal X-ray diffraction experiments. NMR and resistivity characterization of Ba₈Au₁₆P₃₀ indicated paramagnetic metallic properties with a room-temperature resistivity of 1.7 m惟 cm. Ba₈Au₁₆P₃₀ exhibits a low total thermal conductivity (0.62 W m^鈥? K^鈥?) and an unprecedentedly low lattice thermal conductivity (0.18 W m^鈥? K^鈥?) at room temperature. The values of the thermal conductivity for Ba₈Au₁₆P₃₀ are significantly lower than the typical values reported for solid crystalline compounds. We attribute such low thermal conductivity values to the presence of a large number of heavy atoms (Au) in the framework and the formation of multiple twinning interfaces and antiphase defects, which are effective scatterers of heat-carrying phonons.