Enhancing Thermoelectric Properties of Si 80 Ge 20 Alloys Utilizing the Decomposition of NaBH 4 in the Spark Plasma Sintering Process

Ali Lahwal, Xiaoyu Zeng, Sriparna Bhattacharya, Menghan Zhou, Dale Hitchcock, Mehmet Karakaya, Jian He, Apparao M. Rao and Terry M. Tritt
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Ali Lahwal: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
Xiaoyu Zeng: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
Sriparna Bhattacharya: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
Menghan Zhou: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
Dale Hitchcock: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
Mehmet Karakaya: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
Jian He: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
Apparao M. Rao: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA
Terry M. Tritt: Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA

Energies, 2015, vol. 8, issue 10, 1-13

Abstract: The thermoelectric properties of spark plasma sintered, ball-milled, p -type Si 80 Ge 20 -(NaBH 4 ) x (x = 0.7,1.7 and 2.7), and Si 80 Ge 20 B 1.7-y -(NaBH 4 ) 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 NaBH 4 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 NaBH 4 decomposed into Na , B , Na 2 B 29 , and H 2 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 Na 2 B 29 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 Si 80 Ge 20 -(NaBH 4 ) 1.7 and Si 80 Ge 20 -B 1.5 (NaBH 4 ) 0.7 at 1100 K as compared to the p -type B-doped Si 80 Ge 20 material used in the NASA’s radioactive thermoelectric generators. This single-step “doping-nanostructuring” procedure can possibly be applied to other thermoelectric materials.

Keywords: SiGe; thermoelectric; spark plasma sintering; power factor; thermal conductivity (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2015
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