Study On The Processing Parameters Of Plasma Activated Sintering And Thermoelectric Properties For Bi₂Te₃-based Bulk Materials

Thermoelectric material is a functional material that can be used to convert thermal energy into electrical energy directly with carriers. It has a long performance life and good stability and environmental benign. So it has been used in many fields, especially in thermoelectric power generating and cooling for electric devices. And as one of the best thermoelectric material around room temperature, Bi₂Te₃ based thermoelectric material are extensively used as Peltier cooler for microelectronic devices, photoelectronic devices, biologic slug, medical appliance, military equipment and so on. However, its low thermoelectric figure of merit restricts its applications. The improvement of its thermoelectric figure of merit has become a hot spot of research. With the development of nanotechnology and related thermoelectric theory, we can solve the problem on the basis of novel syntheses methods or low dimension material. As a novel sintering method, the progress of plasma activated sintering (PAS) shows a promising future of high performance of thermoelectric material, it's a sintering method to prepare bulk material, and has many advantages such as fast warming, short sintering time, rapid cooling sintering atmosphere controllable, energy saving, environmental protection and so on, and also it has shown great superiority over traditional sintering method on the preparation of nano-materials and composite materials, in a word it is a novel sintering method of great application value and broad prospects.This dissertation is the follow-up work of Bi₂Te₃ based material prepared by combining mechanical alloying(MA) and plasma activated sintering(PAS) and its thermoelectric performance testing, the p-type Bi_0.4Sb_1.6Te₃ bulk material had outstanding performance in previous work.The process parameters of the whole process of bulk material preparation were focused on and optimized in this dissertation. The MA parameters were identified as 400r/min for the milling speed, 12h for the milling time and 13:1 for the weight ratio of balls to powder respectively. The pulse current and its lasting time during the PAS process coud greatly affect both the electrical resistivity and Seebeck coefficient of the Bi_0.4Sb_1.6Te₃ bulk material, while the time of sintering just affected the electrical resistivity greatly, not the Seebeck coefficient.A preliminary research on n-type Bi₂Te_2.85Se_0.15 bulk material was also performed, the effect of AgI and CuBr2 dopant to the thermoelectric properties was also studied. Although the electrical resistivity, Seebeck coefficient and thermal conductivity changed obviously, the figure of merit(Z) got no significant improvement.Finally, the full text of research about p-type Bi_0.4Sb_1.6Te₃ and n-type Bi₂Te_2.85Se_0.15 bulk material were summarized, we hoped that the process parameters of the whole process could be more strictly changed, and bulk thermoelectric materials with excellent performance will be prepared by plasma activation sintering, and advice for further research work of PAS was given.