Effect of abnormal grain growth on thermoelectric properties of hot-pressed Bi0.5Sb1.5Te3 alloys

Many efforts have been made to improve thermoelectric figure of merit (ZT) of Bi2Te3-based alloys since they are the most promising materials for near room temperature applications. Among various strategies, forming structures with mixed grain sizes in thermoelectric materials is proven to be an effective one, which could lead to low-resistivity transport channels for charge carriers but meanwhile scatter phonons with different mean free paths effectively. Unlike the traditional methods using the mixture of powders with different sizes, we report that abnormal grain growth is a feasible and convenient approach to obtain the mixed-grain-size microstructure in Bi0.5Sb1.5Te3 alloys. The materials preparation parameters including milling conditions and sintering temperature were carefully studied. It is shown that Bi0.5Sb1.5Te3 alloys with mixed grain sizes can be achieved via ball milling followed by hot pressing at 480 degrees C due to abnormal grain growth. The properties measurements prove the enhancement of thermoelectric performance with a peak ZT of 1.4 at 340 K. This work demonstrates a facile approach to obtain the mixed-grain-size microstructure in Bi0.5Sb1.5Te3 alloys for enhancing thermoelectric properties. (C) 2019 Elsevier B.V. All rights reserved.