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

Energies

Ali Lahwal¹  Xiaoyu Zeng¹  Sriparna Bhattacharya¹  Menghan Zhou¹  Dale Hitchcock¹  Mehmet Karakaya¹  Jian He¹  Apparao M. Rao¹  Terry M. Tritt¹ 

[1] Department of Physics & Astronomy, Clemson University, Clemson, SC 29634, USA; E-Mails:

关键词: SiGe;    thermoelectric;    spark plasma sintering;    power factor;    thermal conductivity;   

DOI  :  10.3390/en81010958

来源: mdpi

【 摘 要 】

The thermoelectric properties of spark plasma sintered, ball-milled, p-type Si₈₀Ge₂₀-(NaBH₄)_x (x = 0.7,1.7 and 2.7), and Si₈₀Ge₂₀B_1.7-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-B_1.5(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.

【 授权许可】

CC BY   
© 2015 by the authors; licensee MDPI, Basel, Switzerland.