Synthesis and thermoelectric properties of semiconducting germanium-based type-II clathrate (K,Sr)₂₄(Ga,Ge)₁₃₆

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• 作者：Kengo Kishimoto^a ; ^{kkishi@yamaguchi-u.ac.jp} ; Suguru Utsunomiya^a ; Koji Akai^b ; Hironori Asada^a ; Tsuyoshi Koyanagi^a
• 关键词：Thermoelectric materials ; Type-II clathrates ; Germanium clathrates ; Carrier compensation ; Band structure ; Group-II elements ; (K ; Sr)24(Ga ; Ge)136
• 刊名：Journal of Alloys and Compounds
• 出版年：2017
• 出版时间：25 February 2017
• 年：2017
• 卷：695
• 期：Complete
• 页码：1610-1616
• 全文大小：1130 K
• 卷排序：695

文摘

Using the group-II element Sr as guest atoms enabled us to compensate the carrier concentrations of Ge-based type-II clathrates, resulting in semiconducting Seebeck coefficients of ∼−100 μV/K. The carrier compensation may be associated with a large contribution from the orbitals of Sr atoms to the conduction band near the Fermi energy. The type-II clathrate samples had a relatively high room-temperature carrier mobility of ∼ 50 cm2 V−1 s−1 because of a small inertial mass. However, the minimum lattice thermal conductivities were 13 mW cm−1 K−1, which was almost a double of the theoretical minimum value of Ge. The crystal structure analysis indicates that the rattling effect was not so strong in the clathrates. As a result, the maximum dimensionless figure of merit was 0.43 at 800 K.