| Thermoelectric (TE) materials, as a new energy conversion form, provide a safety and direct conversion of electricity and thermal energy. Due to the advantages of TE devices based on TE materials'Seebeck effect and Peltier effect, such as simple structure, abrasion free, no moving parts, quite, small, quickly respond, safe, maintenance free and etc., they have very extensive application prospects. As the best TE materials around room temperature, both the p-type and n-type Bi2Te3 based alloys have a nice thermoelecric performance and a maximum figure of merit ZT near 1. It is still the best commercial and the most widely used TE materials near room temperature in this day and age.Both theoretical calculations and experimental results indicate that doping, alloying and various new powder preparation technologies could introduce effective composition optimization and structure modulation into Bi2Te3 alloys, and improve its transport properties. Recently, with the rise of nano technology, quantum effect and energy filtering effect of nano-state also provide a possible enhancement of Seebeck coefficient. In this study, we choose p-type Bi-Sb-Te alloy as the research target, try to improve the properties of materials through the grain refinement, introducing nano-scale structure modulation into the alloys. On that basis, the new "hot deformation recrystallization introduced in situ nano structure" method have been developed. Meanwhile, doping, alloying and composition introduced structure modulation of Bi-Sb-Te alloys have been simply studied, and the primary research results on large scale bulk sintered alloys and TE modules also have been briefly introduced. The main results are listed as below:1. Hot deformation recrystallization could effectively introduce nano-structure modulation and crystal defects into the materials and improve the TE transport properties. The 5 - 10 nm in situ nanostructure and high density of crystal defects could reduce the material thermal conductivity and effectively improve Seebeck coefficients of the material. The maximum room temperature ZT～1.5 have been achieved after hot deformation. Compared to the'bottom up" nano materials preparation methods, such as ball milling, melt spinning, low temperature solvothermal method and etc., hot deformation is a new simple, highly repeatable, and effective "top down" method for the nanostructure modulation and properties optimization of bulk Bi-Sb-Te alloys. Moreover, TE properties of both the sintered bulk p-type alloys and zone melting ingots could be improved by hot deformation methods, and the results are highly repeatable and stable.2. The anisotropy of structure and transport properties in bismuth tellurium based alloys has always been a focus of the research work. As the electrical and thermal conductivities were measured along different directions, the ZT could be overestimated up to 60%. In the work, p/n type bismuth tellurium based large scale bulk alloys with homogeneous composition & structure have been prepared by spark plasma sintering (SPS) technology. The relationship between the anisotropic structure and the anisotropic thermal conductivities has been established, which could effectively avoid the underestimation of the thermal conductivity. At the same time, the study also implied that the n-type alloy are much easier to be (001) textured than the p-type one under the same fabrication condition.3. Melt spinning and spray casting could effectively refine the grain sizes, reduce the thermal conductivity and affect thermoelectric transport properties. The minimum lattice thermal conductivities could reached 0.3～0.4 Wi-1K-1 after the grain refinement. Thermoelectric properties of spray casted samples changed a little during the temperature increasing. ZT～1.2 was achieved by this technique, and the value stayed above 1.0 within the measuring temperature range.4. The carrier concentration and electrical conductivity were enhanced by doping and alloying, which additionally shifted the intrinsic excitation temperature and the maximum value of ZT to high temperature range. Bergman-Fel model have been used to simply analyse the TE properties of (Ag0.92b1.08Te2)Bi0.5Sb1.5Te3)1-x alloys. Ag2Te alloying can effectively reduce the lattice thermal conductivity of Bi-Sb-Te alloy, which implied the composition change may also affect the structure of the materials5. SPS technology could prepare Bi-Sb-Te bulk alloy with nice properties in lower temperature/pressure and shorter time. Large scale sintered Bi2Te3 based bulk alloy have been prepared by SPS. After the scale-up process, the ZT value of p-type materials could still be around 1. Meanwhile, study of the thermal mechanical properties of Bi2Te3 based alloys identified that these materials will remain structure stable below 500 K. After 500 K, Bi2Te3 alloys could be soften.
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