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Energies 2015, 8(10), 10958-10970; doi:10.3390/en81010958

Enhancing Thermoelectric Properties of Si80Ge20 Alloys Utilizing the Decomposition of NaBH4 in the Spark Plasma Sintering Process

1
Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
2
Clemson Nanomaterials Center, and Center for Optical Materials Science and Engineering Technologies, Clemson University, Clemson, SC 29625, USA
3
Department of Materials Science & Engineering, Clemson University, Clemson, SC 29634, USA
*
Authors to whom correspondence should be addressed.
Academic Editor: Shi Xue Dou
Received: 17 July 2015 / Revised: 8 September 2015 / Accepted: 14 September 2015 / Published: 29 September 2015
(This article belongs to the Special Issue Thermoelectric Energy Harvesting)
View Full-Text   |   Download PDF [1569 KB, uploaded 29 September 2015]   |  

Abstract

The thermoelectric properties of spark plasma sintered, ball-milled, p-type Si80Ge20-(NaBH4)x (x = 0.7,1.7 and 2.7), and Si80Ge20B1.7-y-(NaBH4)y (y = 0.2 and 0.7) samples have been investigated from 30 K to 1100 K. These samples were prepared by spark plasma sintering of an admixture of Si, Ge, B and NaBH4 powders. In particular, the degasing process during the spark plasma sintering process, the combined results of X-ray powder diffraction, Raman spectroscopy, Hall coefficient, electrical resistivity, and Seebeck coefficient measurements indicated that NaBH4 decomposed into Na, B, Na2B29, and H2 during the spark plasma sintering process; Na and B were doped into the SiGe lattice, resulting in favorable changes in the carrier concentration and the power factor. In addition, the ball milling process and the formation of Na2B29 nanoparticles resulted in stronger grain boundary scattering of heat-carrying phonons, leading to a reduced lattice thermal conductivity. As a result, a significant improvement in the figure of merit ZT (60%) was attained in p-type Si80Ge20-(NaBH4)1.7 and Si80Ge20-B1.5(NaBH4)0.7 at 1100 K as compared to the p-type B-doped Si80Ge20 material used in the NASA’s radioactive thermoelectric generators. This single-step “doping-nanostructuring” procedure can possibly be applied to other thermoelectric materials. View Full-Text
Keywords: SiGe; thermoelectric; spark plasma sintering; power factor; thermal conductivity SiGe; thermoelectric; spark plasma sintering; power factor; thermal conductivity
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Lahwal, A.; Zeng, X.; Bhattacharya, S.; Zhou, M.; Hitchcock, D.; Karakaya, M.; He, J.; Rao, A.M.; Tritt, T.M. Enhancing Thermoelectric Properties of Si80Ge20 Alloys Utilizing the Decomposition of NaBH4 in the Spark Plasma Sintering Process. Energies 2015, 8, 10958-10970.

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