多填充和纳米复合对n型方钴矿热电性能的提升

The thermoelectric (TE) materials are a very good candidate to achieve efficient usage of energy. Among promising thermoelectric materials, filled skutterudites based on CoSb3 have attracted wide attention not only because of their promising dimensionless figure-of-merit, but also very good mechanical properties. Current strategies to improve the figures of merit of CoSb3 based filled skutterudites are focusing on the optimization of the power factor through substitutional doping, optimal filling and reduction in thermal conductivity using mass fluctuation phonon scattering via solid-solution alloying and nanostructuring. However, the transport parameters are interdependent and, often,attempts to maximize one parameter have deleterious effect on the other parameters.In this study, we focus on n-type CoSb3 compound. The TE properties are expected to be improved by multi-filling,grain size reduction, and ex-situ second phase of metal nanoparticles to obtain CoSb3 based nanocomposites. We first explore the feasibility of filled skutterudites with first principle calculation, synthesize filled skutterudites by combing solid state reaction with spark plasma sintering (SPS) technique. The relationship between different fillers and thermoelectric properties are studied to achieve optimal multi-filled skutterudite. Then we consider it as a matrix and employ ball milling to reduce grain size down to 100nm and disperse metal nanoparticles to form CoSb3 nanocomposites.The influence of microstructure of this final product on thermoelectric properties are investigated. This method is a good example of how multi-filling and nanostructuring can be used to achieve the desirable electronic properties while maintaining a low thermal conductivity in skutterudite based thermoelectrics.

方钴矿热电材料近年来在性能方面不断得到提高，主要是通过结构低维化和掺杂两种手段，但是由于热电参数之间的互相约制关系，这两种手段往往不能实现电声性能的同时改进。本研究主要通过多原子复合填充、结构纳米化（降低晶粒尺寸）和非原位引入金属纳米第二相的方法，形成多原子填充方钴矿纳米复合物来改善CoSb3基方钴矿的热电性能。本项目事先根据第一性原理计算，结合具体实验，优化多原子填充种类、组合方式及其相应的填充分数，深入了解填充原子对体系组分、晶体结构和热电性能的影响规律，确定优化的多原子填充方钴矿。以此为基体，采用球磨技术，降低基体晶粒尺寸至100nm以下，实现基体结构纳米化。然后非原位引入金属纳米第二相得到方钴矿纳米复合物，系统研究最终产物的组分与微结构对材料电声性能的影响规律，制备出具有良好的电传输特性,同时具有低的热导率的高性能方钴矿热电材料，推动方钴矿热电器件的商品化和产业化。

本项目以中温热电应用最重要的体系方钴矿材料作为研究对象，采用传统的固相反应法结合高能球磨与热压烧结，制备了Ba填充的n型方钴矿的纳米复合物。采用球磨技术，降低了基体晶粒尺寸至100nm以下，实现基体结构纳米化。非原位引入金属纳米Ag颗粒和不同形态的TiO2第二相成功获得了方钴矿纳米复合物。通过对其热电性能的系统研究，揭示了最终产物的组分与微结构与复合纳米第二相的含量、形貌和尺寸大小与分布对材料电声性能的影响规律，制备出具有良好的电传输特性，同时具有低的热导率的高性能n型方钴矿热电材料。金属纳米Ag颗粒和不同形态的TiO2第二相制备的方钴矿纳米复合物ZT值分别达到1.4与1.2，有力大幅度推动方钴矿热电器件的商品化和产业化。