通常一個好的熱電材料必須具備良好的電導係數及Seebeck係數，以及低熱導係數，這是一般傳統合金所無法具備的。相對於單一主元素之傳統合金，具多主元素之高熵合金係一嶄新的冶金概念。在目前已開發之部分高熵合金系統業已展現出極優異之機械性質與化學性質，然而高熵合金之電性質與熱電性質則尚未有詳盡之探討。本研究以half-heusler三元合金當作出發點，利用真空電弧熔煉製作合金，經由熱處理後，量測其熱電性質，找到兩個具有發展潛力的系統：ZrTiSnSiNi2、ZrTiSnGeNi2，室溫下熱電優值ZT分別為0.02與0.045。當在中高溫的範圍(250~300℃)時功率因子(S2/ρ)約可增加3~4倍，將成份改質為Zr0.9Ti0.9Nb0.2SnSiNi2，結果顯示室溫下的熱電優值ZT約為0.078。利用X光結晶繞射(XRD)、掃瞄式電子顯微鏡(SEM)與能量散佈光譜儀(EDS)鑑定出此二多元合金系統為具有半導體與金屬組成相的複合材料。

A good thermoelectric material requires high Seebeck coefficient (S) and electrical conductivity (σ) but low thermal conductivity (κ), which are not common found in traditional metallic alloys. As compound with traditional metallic alloy, high entropy alloy of multi constituent element is a newly developed metallurgical concept. A variety of different forms of the multi-element alloys have been demonstrated to possess superior mechanical and chemical properties. However, the electrical and thermoelectric properties of the multi-element alloys have not been thoroughly explored yet. In this study, multi-element alloys were prepared by arc-melting and thermal annealing. Their thermoelectric properties were characterized after appropriate sample preparation. We find two multi-element alloy systems based on half-Heusler structure：ZrTiSnSiNi2 and ZrTiSnGeNi2. The thermoelectric figure of merits (ZT , Z= S2/(ρ×κ)) of these multi-element alloys were equal to be 0.02 and 0.045, respectively, at room temperature. These multi-element alloys showed 3 times increase in power factor (S2/ρ) in the middle temperature range (250℃ to 300℃). By adding Nb element into the alloy forming Zr0.9Ti0.9Nb0.2SnSiNi2, the thermoelectric figure of merit was found to be 0.078 at room temperature. The multi- element alloys were identified to be a composite material containing semiconductor-like phase and metallic-like phase by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS).

1. H. J. Goldsmid, in CRC Handbook of Thermoelectrics, D. M. Rowe Ed., Boca Raton, Florida, 1995 Chap. 3
2. K. H. Huang, “A study on multicomponent alloy systems containing equal-mole elements”, Master thesis, Dept. Materials Science and Engineering, National Tsing-Hua University, June, 1996
3. K. T. Rai, “Microstructures and properties of multi component alloy system with equal-mole elements”, Master thesis, Dept. Materials Science and Engineering, National Tsing-Hua University, June, 1998
4. Y. H. Sheu, “A study on multicomponent alloy system with equal-mole FCC or BCC elements”, Master thesis, Dept. Materials Science and Engineering, National Tsing-Hua University, July, 2000
5. Jien-Wei Yeh, Swe-Kai Chen, Su-Jien Lin, Jon-Yiew Gan, Tsung-Shune Chin, Tao-Tsung Shun, Chun-Huei Tsau, and Shou-Yi Chang, “Nanostructured high-entropy alloys with multiple principal elements：Novel alloy design concept and outcomes” Adv. Eng. Mater Vol 6, p299 (2004)
6. G. S. Nolas, G. A. Slack, American Scientist, Vol. 89 (2001)
7. G. A. Slack, in CRC Handbook of Thermoelectrics, edited by D. M. Rowe(Chemical Rubber, Boca Raton, FL, 1995),Chap. 34
8. G. S. Nolas,etc. “A comparison of projected thermoelectric and thermionic refrigerators” J. Appl. Phys., 4066~4070(1999)
9. Francis J. DiSalvo,“Thermoelectric cooling and power generation” Science. Vol. 285, 703 (1999)
10. C.S. Lue, Y.-K. Kuo, “Thermoelectric properties of the semimetallic Heusler compounds Fe2-xV1+xM (M= Al, Ga)” Phys. Rev. B 66, 085121 (2002).
11. B.C. Sales, D. Mandrus, and R.K. Williams,“Filled skutterudite antimonides: A new class of thermoelectric materials” Science 272, 1325 (1996).
12. Heinrich Hohl, Art P Ramirez, Claudia Goldmann, Gabriele Ernst, Bernd W¨olfing and Ernst Bucher. J. “Efficient dopants for ZrNiSn-based thermoelectric materials”Phys.: Condens. Matter 11 1697–1709 (1999)
13. Q. Shen, L. Chen, T. Goto and T. Hirai, J. Yang and G. P. Meisner, C. Uher “Effects of partial substitution of Ni by Pd on the thermoelectric propertiesof ZrNiSn-based half-Heusler compounds” Appl. Phys. Lett., 79, p4165 (2001)
14. C. Uher, J. Yang, S. Hu, D. T. Morelli, and G. P. Meisner“ Transport properties of pure and doped MNiSn (M=Zr, Hf)” Phys. Rev. B, 59 p.8615, 1999
15. K. Mastronardi, D. Young, C.-C. Wang, P. Khalifah, A. P. Ramirez, and R. J. Cava, “Antimonides with the half-Heusler structure: New thermoelectric materials” Appl. Phys. Lett., 74, p.1415, 1999
16. Semiconductors and Semimetals, vol 70：Recent Trends in Thermoelectric Materials Research, Part Two,edited by Terry Tritt,Chap2 (2000)
17. “Standard Test Methods for Measuring Resistivity and Hall Coefficient and Determining Hall Mobility in Single-Crystal Semiconductors, ”ASTM Designation F76,Annual Book of ASTM Standards, Vol. 10.05 (2000).
18. Cahill, D. G. (1990). "Thermal conductivity measurement from 30 to 750 K:the 3ω method." Review of Scientific Instruments 61(2).
19. Cahill, D. G. (1997). "Heat transport in dielectric thin films and at solid-solid interfaces." Microscale Thermophysical Engineering 1: 85-109.
20. Cahill, S.-M. L. a. D. G. (1997). "Heat transport in thin dielectric films." Journal of Applied Physics 81(6): 2590-2595.