Bi2Te3合金基纳米复合体系中能量过滤效应及提升其热电性能途径的实验研究和探索

Bi2Te3 alloys are not only 3D topological insulators (TI), but also currently the best thermoelectric materials near room temperatures. Although its thermal conductivity is lowered to near that of amorphous solids by alloying and using nanostructures, the improvements of their thermoelectric figure of merit (ZT) are still limited. In order to elevate their thermoelectric performance, one has to explore new routes to enhance their power factor PF (specially thermopower); While the key issue to increase PF is to enhance thermopower through intensifying the energy filtering effect of carriers. Based on our previous investigations, we shall prepare Bi2Te3 alloy-based nanocomposites embedded with semiconducting nanoparticles in the present project. The energy filtering effect can be enhanced and thermopower can be increased in terms of synergetic scattering of interface potential barriers (or wells) formed in the matrix due to the dispersed nanoparticles and other scatterers. Moreover, in terms of conducting (internal) surfaces of 3D TI ,the negative effect on the carrier mobility of the scattering by the interface potentials can be reduced or counteracted, so that the PF can be effectively raised. Simultaneously,their thermal conductivity can be decreased greatly through scattering of phonons with middle and long wave-length (which contribute mainly to thermal conductivity in alloys) by the large number of the nanoparticles and phase boundaries. Through match of various dispersed phases with the alloy matrix, we will investigate the effect of the combinations of same type and different types of semiconductors, interface potential height (or depth), the size of the nanoparticles, particle content and doping in guest phases on thermoelectric properties of the nanocomposite systems, so that we can approach the relevancy of energy filtering effect with parameters of microstructures and electronic structures, such as species of the dispersed phases and their composition, etc. , and reveal their influence laws. All these will provide us with scientific evidence to elevate greatly the thermoelectric performance of Bi2Te3 alloys.

Bi2Te3合金既是三维拓扑绝缘体，又是当今室温附近最好的热电材料。目前通过纳米化等措施已使其晶格热导率接近非晶极限，但其热电性能提高仍有限。为大幅提升其热电性能，必须提高功率因子，而增强载流子的能量过滤效应提高热电势是提升功率因子的重要途径。本项目以前期工作为基础，以该合金为基体复合半导体纳米粒子，利用基体中形成的异质结界面势垒(阱)的散射来增强能量过滤效应提高热电势，同时利用三维拓扑绝缘体高迁移率的(内)表面导电层减小或抵消界面势散射对迁移率的负面影响，以提高功率因子；同时利用众多纳米粒子和相界面增强对热导有贡献的中、长波声子的散射，以大幅降低热导。通过研究分散相与基体匹配、同型异型复合、界面势高(深)度、粒子尺寸、含量以及异相掺杂等对复合体热电性质的影响，揭示能量过滤效应与分散相种类、粒径等微结构和电子结构的关联性，并阐明其内在机制,为大幅提升Bi2Te3合金的热电性能提供科学依据。

Bi2Te3合金是目前室温附近最好的热电材料, 但其热电性能仍有待提高。为大幅提升其热电性能，本项目探索和研究利用载流子的能量过滤效应提高热电势及其热电性能的途径。在本项目的支持下，我们分别研究了Cu3SbSe4、Cu2Se、CuO、beta-Zn4Sb3、 PbSe、 GNs、α-SiO2、α-Si3N4 等不同禁带宽度的材料作为纳米添加相与p-型BiSbTe合金基体复合以形成纳米复合体系，借助界面势的散射以增强载流子的能量过滤效应。通过研究复合体系的热电性能与分散相的种类及其粒度、微结构以及含量等之间的关系发现，合适的禁带宽度第二相材料在一定的含量范围内可以有效的调控复合体系的热、电输运性质，实现能量过滤效应增强功率因子，同时散射声子；同时发现，界面势能有效抑制少子输运从而大幅提升高温区的热电势、降低双极效应引起的热导，进而大幅优化材料的高温区热电性能。本项目通过合理选择第二项、控制其粒度以及分布和密度，成功的获得了几种ZT>1.5的复合材料（Cu3SbSe4、Cu2Se、 PbSe作为添加相）。该材料在300 K至500 K的宽广温度范围内其平均ZT最高达1.4，使得该材料在低级废热回收应用上具有诱人的应用前景。研究结果在Journal of Materials Chemistry A，Applied Physics Letters, Energy等国际期刊上发表了标注资助的SCI论文38篇，授权发明专利2项。另外，培养毕业博士生2名，毕业硕士生3名。