@article{3f9dd00f8f154b57b9886c69e5fa7ab6,
title = "Enhancement of thermoelectric efficiency in type-VIII clathrate Ba 8Ga16Sn30 by Al substitution for Ga",
abstract = "Single-crystalline samples of type-VIII clathrate Ba8Ga 16-xAlxSn30 (0≤x≤12) were grown from Sn flux to characterize the structural and thermoelectric properties from 300 to 600 K. The lattice parameter increases by 0.5% as x is increased to 10.5 whose value is the solubility limit of Al. The Seebeck coefficients of all samples are largely negative and the absolute values increase to approximately 300 μV/K on heating to 600 K. This large thermopower coexists with the metallic behavior in the electrical resistivity. The values of resistivity for 1≤x≤6 at 300 K are in the range 3.3-3.8 mωcm which is 70% of that for x=0. As a result, the power factor for x=4 and 6 has a rather large maximum of 1.83× 10-3 W/m K2 at 480 K. The thermal conductivity stays at a low level of 0.72 W/mK up to 480 K, and the sample with x=6 reaches a ZT value of 1.2 at 500 K.",
author = "Shukang Deng and Yuta Saiga and Koichiro Suekuni and Toshiro Takabatake",
note = "Funding Information: We would like to thank Y. Kono, N. Ohya, and T. Taguchi for thermal conductivity measurements, and Y. Shibata for EPMA performed at Natural Science Center for Basic Research and Development, Hiroshima University. We acknowledge K. Akai for valuable discussion. This work was supported by New Energy and Industrial Technology Development Organization (NEDO, Grant No. 09002139-0) and Grant-in-Aid for Scientific Research from MEXT of Japan, Grants No. 1824032, No. 19051011, and No. 20102004. Table I. Crystal compositions, lattice parameter a , Hall coefficient R H , carrier density n , and carrier mobility μ H at room temperature for Ba 8 Ga 16 − x Al x Sn 30 samples. Starting compositions Ba:Ga:Al:Sn are 8 : ( 16 − x ) : x : 50 . Sample x Crystal composition Lattice parameter a ( {\AA} ) Carrier density n ( 10 19 / cm 3 ) Hall coefficient R H ( cm 3 / C ) Carrier mobility μ H ( cm 2 / V s ) Ba Ga Al Sn Ga + Al + Sn 0 7.96 15.9 0 30.1 46.0 11.602(1) 4.23 −0.146 27.8 1 7.90 15.0 0.96 30.2 46.1 11.604(1) ⋯ ⋯ ⋯ 2 7.97 13.9 1.95 30.2 46.0 11.609(1) 3.94 −0.157 45.4 4 7.97 12.0 3.83 30.2 46.0 11.612(1) ⋯ ⋯ ⋯ 6 8.02 10.1 5.67 30.2 46.0 11.619(1) 4.62 −0.134 40.3 8 8.00 8.19 7.57 30.2 46.0 11.639(1) 4.51 −0.137 33.1 10 7.98 6.21 9.53 30.3 46.0 11.641(1) ⋯ ⋯ ⋯ 12 7.99 5.23 10.5 30.3 46.0 11.659(1) ⋯ ⋯ ⋯ FIG. 1. Unit cell of type-VIII clathrate Ba 8 Ga 16 Sn 30 viewed along the [100] direction. The large circles denote guest Ba atoms and small circles denote cage atoms of Ga and Sn. FIG. 2. As grown single crystal of type-VIII clathrate Ba 8 Ga 10 Al 6 Sn 30 . FIG. 3. Powder XRD patterns for Ba 8 Ga 16 − x Al x Sn 30 samples taken with Cu K α radiation at room temperature. The inset shows the lattice parameter as a function of Al composition of the crystals. FIG. 4. Temperature dependence of electrical resitivity ρ for type-VIII clathrate Ba 8 Ga 16 − x Al x Sn 30 . FIG. 5. Temperature dependence of Seebeck coefficient α of type-VIII clathrate Ba 8 Ga 16 − x Al x Sn 30 . FIG. 6. Temperature dependence of power factor P for type-VIII clathrate Ba 8 Ga 16 − x Al x Sn 30 . FIG. 7. Temperature dependence of thermal conductivity κ for type-VIII clathrate Ba 8 Ga 16 − x Al x Sn 30 . FIG. 8. Temperature dependence of dimensionless figure of merit Z T for type-VIII clathrate Ba 8 Ga 16 − x Al x Sn 30 . ",
year = "2010",
month = oct,
day = "1",
doi = "10.1063/1.3490776",
language = "English",
volume = "108",
journal = "Journal of Applied Physics",
issn = "0021-8979",
publisher = "American Institute of Physics Publising LLC",
number = "7",
}