||The crisis of energy shortage and carbon reduction has become an important issue; the green technology is getting more and more attention. The thermoelectric power generator exhibits the advantages of environmental protection and renewable energy. The thermoelectric devices can convert heat energy to electric energy and vice versa. Bismuth telluride (Bi-Te) and antimony telluride (Sb-Te)-based compounds, which exhibit the highest figure of merit (ZT), are known to be the best thermoelectric materials within the room temperature region and are widely utilized for thermoelectric cooling and generation. In this study, thermoelectric materials were prepared by different processing methods. The characteristics of the obtained thermoelectric materials are investigated. The powder metallurgy method was adopted to fabricate Bi2Te2.7Se0.3 and Bi0.5Sb1.5Te3 thermoelectric materials via the ball milling, cold pressing, and sintering processes. The effects of sintering time and temperature on the thermoelectric properties are investigated and discussed for the Bi2Te2.7Se0.3 and Bi0.5Sb1.5Te3 thermoelectric materials. On the other hand, Bi2Te3 and Sb2Te3-based thin films were prepared by thermal evaporation method on the silicon substrates. The influences of substrate temperature and annealing temperature on the surface morphology, crystal structure and thermoelectric properties of thin films are investigated. Further, the Ag-doped Bi2Te3 and Sb2Te3 thin films are also fabricated by co-evaporation and then annealed. The effects of post annealing on the microstructures and thermoelectric properties of the thin films are evaluated.|
In the study of bulk thermoelectric materials, the Seebeck coefficient of Bi2Te2.7Se0.3 decreased at first and then increased by the increased sintering temperature. Moreover, the results also showed that the thermal conductivity and electrical resistivity exhibited a reversal trend. When the thermal conductivity was increased by the increased sintering temperature, the electrical resistivity was reduced. The calculated PF of 1.074 mW/mK2 was obtained as the sample was sintered at 723K for 2h. The figure of merit (ZT) of 0.31 was obtained at room temperature as the sample was sintered at 648K for 2h. The thermoelectric properties of Bi0.5Sb1.5Te3 showed that the optimal Seebeck coefficient of 300.694 μV/K was obtained as the sample was sintered at 623K for 1h and the resistivity reached the maximum. The figure of merit (ZT) of 0.15 was obtained at room temperature as the sample was sintered at 648K for 3h, in which, the structure showed the rectangular prism crystallization.
Besides, n-type Bi2Te3 and p-type Sb2Te3 thin films were deposited on SiO2/Si substrates using thermal evaporation method in this thesis. The influences of substrate temperature and thermal annealing on the structure, composition, morphology and thermoelectric properties of Bi2Te3 and Sb2Te3 thin films were investigated. As the substrate temperature increased to 150°C, the power factors of n-type Bi2Te3-based and p-type Sb2Te3-based thin films were found to be about 4.89 μW/cm⋅K2 and 3.94 μW/cm⋅K2, respectively. Further, the Ag-doped thin films were fabricated by co-evaporation and the thermal annealing treatment was carried out. The results showed that the Ag-doped Bi2Te3 with a maximized value of power factor of 2.16 μW/cm·K2 could be obtained at the substrate temperature of 100°C and annealing temperature of 250°C (0.5hr). In the Ag-doped Sb2Te3, the thin films exhibited a maximized value of power factor of 19.99 μW/cm·K2 at the substrate temperature of 150°C and annealing temperature of 200°C (0.5hr).