Tuning Thermoelectric Properties of Type I Clathrate K8–xBaxAl8+xSi38–x through Barium Substitution

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• 作者：Fan Sui ; Susan M. Kauzlarich
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：May 10, 2016
• 年：2016
• 卷：28
• 期：9
• 页码：3099-3107
• 全文大小：473K
• 年卷期：0
• ISSN：1520-5002

文摘

The thermal stability and thermoelectric properties of type I clathrate K₈Al₈Si₃₈ up to 873 K are reported. K₈Al₈Si₃₈ possesses a high absolute Seebeck coefficient value and high electrical resistivity in the temperature range of 323 to 873 K, which is consistent with previously reported low temperature thermoelectric properties. Samples with Ba partial substitution at the K guest atom sites were synthesized from metal hydride precursors. The samples with the nominal chemical formula of K_8–xBa_xAl_8+xSi_38–x (x = 1, 1.5, 2) possess type I clathrate structure (cubic, Pm3̅n), confirmed by X-ray diffraction. The guest atom site occupancies and thermal motions were investigated with Rietveld refinement of synchrotron powder X-ray diffraction. Transport properties of Ba-containing samples were characterized from 2 to 300 K. The K–Ba alloy phases showed low thermal conductivity and improved electrical conductivity compared to K₈Al₈Si₃₈. Electrical resistivity and Seebeck coefficients were measured over the temperature range of 323 to 873 K. Thermal conductivity from 323 to 873 K was estimated from the Wiedemann–Franz relation and lattice thermal conductivity extrapolation from 300 to 873 K. K_8–xBa_xAl_8+xSi_38–x (x = 1, 1.5) synthesized with Al deficiency showed enhanced electrical conductivity, and the absolute Seebeck coefficients decrease with the increased carrier concentration. When x = 2, the Al content increases toward the electron balanced composition, and the electrical resistivity increases with the decreasing charge carrier concentration. Overall, K_6.5Ba_1.5Al₉Si₃₇ achieves an enhanced zT of 0.4 at 873 K.