Complex microstructures are found in many thermoelectric materials and can be used to optimize their transport properties. Grain boundaries in particular scatter phonons, but they often impede charge carrier transfer at the same time. Designing grain boundaries in order to offer a conductive path for electrons is a substantial opportunity to optimize thermoelectrics. Here, we demonstrate in TiCoSb half Heusler compounds that Fe-dopants segregate to grain boundaries and simultaneously increase the electrical conductivity and reduce the thermal conductivity. To explain these phenomena, three samples with different grain sizes are synthesized and a model is developed to relate the electrical conductivity with the area fraction of grain boundaries. The electrical conductivity of grain interior and grain boundaries is calculated and the atomic structure of grain boundaries is studied in detail. Segregation engineering in fine-grained thermoelectrics is proposed as a new design tool to optimize transport properties while achieving a lower thermal conductivity.

许多热电材料中都存在复杂的微观结构，可用于优化其传输特性。晶界尤其会散射声子，但它们通常同时会阻碍电荷载流子的转移。设计晶界以便为电子提供导电路径是优化热电学的重要机会。在这里，我们在 TiCoSb 半 Heusler 化合物中证明了 Fe 掺杂剂偏析到晶界，同时增加了电导率并降低了热导率。为了解释这些现象，合成了三个具有不同晶粒尺寸的样品，并开发了一个模型来将电导率与晶界面积分数联系起来。计算了晶粒内部和晶界的电导率，并详细研究了晶界的原子结构。细粒度热电材料中的偏析工程被提议作为一种新的设计工具来优化传输性能，同时实现较低的导热性。