碲化铋基多晶合金热电输运性能的优化

OPTIMIZATION OF THERMOELECTRIC TRANSPORT PROPERTIES OF BISMUTH TELLURIDE-BASED POLYCRYSTALLINE ALLOYS

舒忠

11849411

硕士

物理学

何佳清

2020-05-28

2020-07-15

哈尔滨工业大学

深圳

热电转换技术作为一种绿色环保的新能源技术，能够实现热能与电能的直接相互转换，其能量转换效率取决于材料的无量纲热电优值（ZT值）。碲化铋基热电材料是目前唯一实现商业化应用的室温热电材料，但相对较低的ZT值严重制约了其大规模的工业化应用。本文以Bi0.5Sb1.5Te3和Bi2Te2.7Se0.3分别作为p型和n型碲化铋的研究对象，利用真空熔炼、球磨和放电等离子烧结技术制备碲化铋多晶合金，探索Te化学计量比、掺杂以及金属第二相对其热电输运性能的影响，研究其热电性能改善的机制。本文采用液相烧结技术对名义化学计量比为Bi0.5Sb1.5Te3+x（x=0，0.1，0.2，0.4，0.6）的多晶合金进行研究，点缺陷的减少和烧结过程中的熔融液态Te带来的晶粒滑移重排，这两种机制可以减少载流子输运过程中受到的散射，提高载流子迁移率从而提升热电性能，最终，Bi0.5Sb1.5Te3.4在323 K获得1.2的ZT值，相比Bi0.5Sb1.5Te3提升50%。进一步，ⅣA族元素Sn和Pb被引入碲化铋阳离子位进行受主掺杂，此类掺杂能够有效提高载流子浓度提升电输运性能的同时抑制双极扩散效应，拓展碲化铋材料在不同温度区间下的应用。其中，Sn掺杂能够在一定程度范围内提高载流子浓度，优化材料在室温附近的热电优值，得到最佳配比(Bi0.25Sb0.75)1.97Sn0.03Te3。在此基础上，Pb掺杂则可以进一步大幅改变载流子浓度，抑制本征激发，使材料的服役温度向高温推移，(Bi0.25Sb0.75)1.97Sn0.02Pb0.01Te3在423 K获得1.2的ZT值。在实际应用中，热电器件需要性能相近的p型材料和n型材料搭配才能发挥材料潜力，因此我们对n型碲化铋进行了研究，在球磨过程加入不同含量的Sb单质分散在Bi2Te2.7Se0.3中形成金属第二相，金属半导体之间的肖特基势垒过滤低能载流子的同时增强对低频声子的散射，Sb含量为5 wt.%时实现400 K下1.3的ZT值，相对于纯样提升40%，并在整个测试温度范围内增强热电性能。

Thermoelectric conversion technology, as a green and environment-friendly new energy technology, can directly convert heat and electricity or vice versa, and its energy conversion efficiency depends on the dimensionless figure-of-merit (ZT value). Bismuth telluride-based thermoelectric (TE) materials are the only thermoelectric material for commercial application at room temperature, but the relatively low ZT value seriously limits its industry application. In this paper, Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 were used as research objects of p-type and n-type bismuth telluride materials, respectively. The polycrystalline bismuth telluride materials were synthesized by vacuum melting, ball milling and spark plasma sintering technology. We investigated the influence of stoichiometry of Te, doping, and the second metal phase on its electrical and thermal transport properties and explored the mechanism about the improvement of TE performance.We investigated polycrystalline alloy with nominal stoichiometric Bi0.5Sb1.5Te3+x (x=0, 0.1, 0.2, 0.4, 0.6) by liquid phase sinter technique. The reduction of point defects and matrix grains rearrangement with the help of molten liquid Te in sintering process, both mechanisms can reduce the carrier scattering which can increase the carrier mobility and improve the thermoelectric performance. As a result, ZT value of 1.2 is obtained for Bi0.5Sb1.5Te3.4 at 323 K, 50% increment compared with Bi0.5Sb1.5Te3. Further, group ⅣA elements Sn and Pb were doped into the bismuth telluride cation site, and the analysis showed that such acceptor dopant can effectively improve carrier concentration and thus the electrical transport properties. And the bipolar effect is also suppressed, so the application temperature ranges of bismuth telluride material has been expanded. Specifically, Sn doping can slightly increase the carrier concentration, enhance the figure of merit of the material near room temperature, and obtain the optimal ratio (Bi0.25Sb0.75)1.97Sn0.03Te3. Based on this result, Pb doping can significantly enhance carrier concentration, and suppress the intrinsic excitation, thus the work temperature of the material has been shifted to higher temperature. As a result, (Bi0.25Sb0.75)1.97Sn0.02Pb0.01Te3 can obtain a ZT value of 1.2 at 423 K. In practice, thermoelectric devices simultaneously require the p-type material and n-type material with similar properties. Therefore, we still investigated the n-type bismuth telluride, different contents of Sb were dispersed into Bi2Te2.7Se0.3 during ball milling process to form second metal phase. The Schottky barrier between metal and semiconductors filtered low energy carriers, at the same time, it enhances the scattering of low-frequency phonons. When the Sb content is 5 wt.%, the ZT value at 400 K is 1.3，40% increment compared with Bi2Te2.7Se0.3 and the thermoelectric performance is enhanced over the entire test temperature range.

热电材料 碲化铋 热电性能 液相烧结 掺杂 金属第二相

thermoelectric material bismuth telluride thermoelectric properties liquid phase sintering doping secondary metallic phase

中文

联合培养

南方科技大学

舒忠. 碲化铋基多晶合金热电输运性能的优化[D]. 深圳. 哈尔滨工业大学,2020.