声子阻隔及载流子能量过滤——提升新型无Pb(Te)金属间化合物Cu3SbSe4热电性能的探索性研究

The burgeoning thermoelectric material Cu3SbSe4 has the figure of merit, ZT, 1.1 at 700K by doping. Although its thermal conductivity is lowered to near the theory value 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 Cu3SbSe4 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. 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 intermetallic compound matrix, we will investigate the effect of the combinations of same type of semiconductors, interface potential height (or depth), the size of the nanoparticles, particle content and doping in guest phases on thermoelectric properties of the composite 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 intermetallic compound Cu3SbSe4.

新型无铅无碲金属间化合物Cu3SbSe4是一种很有潜力的中温热电材料，通过纳米化和掺杂已使其晶格热导率接近理论最小值，其在700K的热电优值为1.1。如何进一步大幅提升其热电性能是极具挑战性的难题。在增强声子散射的同时，提高载流子的能量过滤效应以增强功率因子是提升ZT值的重要举措。本项目以前期工作为基础，以掺杂的Cu3SbSe4为基体、以不同带隙的几种半导体纳米粒子为分散相形成纳米复合体系，借助不同的带隙匹配形成的不同高度异质结界面势垒(阱)的散射来增强能量过滤效应提高热电势，同时利用众多纳米粒子本身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。通过研究具有不同分散相与基体匹配、界面势垒高度(垒阱深度)、粒子尺寸、含量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Cu3SbSe4的热电性能提供科学依据。

金属间化合物 Cu3SbSe4 体系是一类新型的中温热电材料。它填补了目前最好的常温热电材料 Bi2Te3 基合金和高温热电材料 SiGe 的热电性能上的空缺，完全有可能替代 PbTe 合金及在高温下的易分解升华和具有低温相变的Zn4Sb3。另外，大多数的余热温度在 100－400ºC，而该温度区间正是 Cu3SbSe4高热电性能区间，因此它的未来应用前景十分看好。我们通过掺杂Sn或Ge优化Cu3SbSe4 的载流子浓度 。在此基础上， 选 取 热 电 性 能 优 越 的 Cu3Sb0.96Sn0.04Se4或Cu3Sb0.94Ge0.06Se4为基体，将热电性能优越的多尺度第二相AgSb0.98Sn0.02Se2、AgSb0.98Ge0.02Se2或Cu3Sb0.96Sn0.04Se4-xSx引入基体材料，形成纳米复合材料。纳米相Cu3Sb0.94Sn0.06Se2.5S1.5 的引入增强了界面散射，导致了极低的晶格热导率。对于Cu3Sb0.96Sn0.04Se4–3% Cu3Sb0.94Sn0.06Se2.5S1.5.复合材料获得了0.87的高ZT。将AgSb0.98Sn0.02Se2和AgSb0.98Ge0.02Se2分别引入Cu3Sb0.96Sn0.04Se4或Cu3Sb0.94Ge0.06Se4基体中，同时实现了功率因子的提升和热导率的降低，最大ZT分别达到1.17和1.23，降低的热导起源于多尺度第二相的引入导致的散射的增强，而增强的功率因子归结于载流子迁移率的增加。我们的工作显示AgSb0.98Sn0.02Se2的引入可极大优化Cu3SbSe4的热电性能。目前，我们获得的ZT是这一体系报道的最高值。