ABSTRACT
The history of V2–VI3 compounds for thermoelectric application near-room temperature started from Bi2Te3 and later moved to its alloys with element Sb at Bi site and Se at Te site.1–3 The early works mainly focused on the well-grown single crystals or casted ingots, which were already well reviewed by many authors over the past decades.4–6 However, the Bi2Te3-based ingots are mechanically brittle due to the intrinsic laminar crystalline structure characterized with van der Waals bonds. In contrast, their polycrystalline counterparts were proved to be more mechanically robust because the grain boundaries work well as a block to the propagation of fracture cracks.7 , 8 The decreased lattice thermal conductivity was widely observed in both the p-type (Bi, Sb)2Te3 and n-type Bi2(Te, Se)3 polycrystalline bulks made by various nanoapproaches. However, the thermoelectric figure of merit (ZT) values of these nanostructured materials were not inevitably enhanced due to various reasons. One of the challenges was the controllable charge carrier concentration, which was sensitive to the native defects, grain boundaries, and protection atmosphere. In this chapter, we will focus our discussion on the latest advances in the performance enhancement and puzzle understandings for the p-type (Bi, Sb)2Te3 and n-type Bi2(Te, Se)3 polycrystalline bulks.
