借助界面势对少子输运过程的散射以提高BiSbTe合金体系高温区热电性能的探索研究

BiSbTe alloy is the best thermoelectric materials near room temperatures, and it is also the only commercialized material used in refrigeration. But, recent study suggests that the alloy can also be used in power generator by using low-grade waste of heat. However, the utilization of this alloy for power generations in high temperature region needs to elevate ZT values at the high temperatures (>350K). Because the band gap of BiSbTe is only ~0.13 eV, the minorities will excite as temperature rises, which leads to decline of thermopower and enhancement of bipolar effect as well as thermal conductivity, giving rise to decrease of ZT. In order to raises high-temperature thermoelectric performance, based on the previous work this study will introduce selenides etc. as dispersed phase to form composites so that one can inhibit the transport of minorities in terms of asymmetric interface potentials. As a result, one can inhibit both the decline of thermopower and occurrence of bipolar effect that would contribute to thermal conductivity. At same time, energy filtering effect could happen by moderate scattering of majorities at the interface potentials so as to enhance the whole thermopower, and thermal conductivity could be reduced further by numerous nanoparticles and phase boundaries to scatter the phonons with middle and long wave length that contribute greatly to thermal conductivity. Through the investigations of the effects of different dispersed phases, their band gaps, their particle sizes, their spatial densities and p-p and n-p incorporations, etc. on interface potentials and thermoelectric properties, such as thermopower and bipolar effect, one can explore their influence law on interface potentials and thermoelectric performances, which can provide us with scientific evidences for elevating high-temperature thermoelectric performance of BiSbTe.

BiSbTe合金是当今室温附近最好的热电材料,也是唯一商业化用于制冷的材料。但最近研究表明该合金有用于低级废热发电的可能。然而，用于该类废热发电必须提高其高温区(>350K)的ZT值。由于BiSbTe合金带隙仅为~0.13 eV，温度升高后少子开始激发，导致热电势下降和双极效应增强、热导升高，使ZT值下降。为提升高温区ZT值，本项目拟在前期工作基础上通过引入硒化物等分散相形成复合体系，借助非对称界面势强烈散射少子抑制其输运，从而抑制热电势下降和双极效应；同时借助该界面势对多子的适度散射产生能量过滤效应增强热电势以及利用众多分散相粒子和相界面强化对热导有贡献的中、长波声子散射，以大幅降低热导。通过研究不同的分散相、其带隙宽度、粒子尺度、空间密度以及同型异型复合等因素对界面势以及最终对复合体热电性质的影响，探寻其影响的规律性并揭示其机理，为大幅提升BiSbTe合金高温区热电性能提供科学依据。

Bi2Te3合金是当今室温附近最好的、也是唯一商业化制冷热电材料。特别是，最近人们认识到可利用该合金用于低级废热发电和利用人体温度为穿戴电子器件(如智能手表)提高电能。然而，用于低级废热发电必须提高其高温区(>350K)的ZT值。由于Bi2Te3合金带隙仅为~0.13 eV，温度升高后少子开始激发，导致热电势下降和增强的双极效应提高热导率，使ZT值在T>~350K快速下降。为提升高温区ZT值，必须抑制少数载流子的输运。在本项目的支持下，在分别研究了Cu3SbSe4、Cu2Se、CuO和Zn4Sb3添加相的基础上，深入研究了GaAs及PbSe等不同禁带宽度纳米相复合对p-型Bi2Te3合金基纳米复合体系，借助形成非对称高界面势垒强烈散射少子抑制其输运，从而抑制少子的贡献及双极效应，大幅提升高温区的热电势、降低双极效应引起的热导率；尤其是，我们提出了散射工程的概念，为如何提高Bi2Te3合金热电性能提高了新的思路。同时，我们成功的获得了几种ZT>1.5的p-型Bi2Te3合金基复合材料(如以PbSe为添加相)，最大ZT值从350K提高至~400K。另外，本项目通过引入同结构纳米相，3D拓扑绝缘体纳米粒子等，利用共格界面和表面态高迁移率的特性，以提升n-型Bi2Te3合金基复合体系中载流子迁移率，从而达到同时提升功率因子和降低晶格热导率的目的，成功获得ZT>1.2几种n-型Bi2Te3合金基复合材料，这将有效促进其商业化应用。截止目前，相关结果在Nanoenergy, Journal of Materials Chemistry A，Composites Part B: Engineering 及ACS Appl. Mater.&Inter等国际期刊上发表了标注资助的SCI论文30篇， 1项发明专利在申请中。此外，培养毕业博士生2名，毕业硕士生2名。