| A2ⅤB3Ⅵ-type(A=Bi,Sb,B=Te,Se) compounds and their alloys are of great thermoelectric properties at room temperature, which found applications in the cooling devices, however, the ZT of these materials are kept at about 1. In recent years, more and more low-dimensional thermoelectric materials are researched, if the materials have nano-structured, the carrier and phonon scattering can be increased, which lead to the increasing of Seebeck coefficient and decreasing of thermal conductivity, and the improvement of the ZT. Therefore, we expect to explorer a method which can prepare a large quantity of nano-structured powder quickly and controllable, and meet the demand of bulk thermoelectric application.In this thesis, Bi2Se3-based thermoelectric compounds are systemically researched, and prepared by solvo-thermal method and low-temperature aqueous chemical route. The effects of prepare technical parameters on phase composition and microstructure and the reaction mechanism of Bi2Se3 nanopowders was discussed. Bi2Se3 bulk material was synthesis by spark plasma sintering technique, and their thermoelectric properties was investigated as well.During the synthesis of Bi2Se3 by solvo-thermal method, the influence of different raw materials, solvent, reaction temperature and time, pH value and surfactant on phase composition and microstructure has been researched, and the best preparing technical parameters were obtained. The Bi2Se3 nanopowders were prepared by solvo-thermal method at 180℃for 24 hours with alkali concentration of 0.25 mol/L, using of Bi(NO3)3·5H2O and Se as reaction raw materials and distilled water and glycol as the solvent which the ratio is 1:1 with 1.0g PVP was dissolved in it. The size of these nanopowders was about 30nm. By investigation and analysis, the mechanism of chemical synthesis of Bi2Se3 was assumed to be a mixture of two mechanisms, namely, atom reaction and ion reaction. The influence of sintering temperature and pressure on the relative density of Bi2Se3 bulk material was discussed and the optimized sintering technique was discovered. The Bi2Se3 bulk material with single phase was sintered by spark plasma sintering at 500℃for 5 min with heating rate of 50℃/min and sintering pressure of 35 MPa to form dense samples. The microstructures of samples had obviously changed before and after sintering. The maximum figure of merit ZT reaches 0.3 at 550 K.The Bi2Se2Te nanopowders with single phase were sintered by solvo-thermal method at 200℃for 36 hours with alkali concentration of 0.25 mol/L, using of distilled water and glycol as the solvent which the ratio is 1:1 with 1.0g PVP was dissolved in it. The size of these nanopowders was about 30nm, and then sintered by spark plasma sintering at 500℃for 5 min to form dense samples. The maximum figure of merit ZT reaches 0.4 at 550 K, which is 30% higher than Bi2Se3 bulk material.The Bi2Se3 thermoelectric compound with ultra-thin hexagonal plate was prepared by low-temperature aqueous chemical route. The influence of different reaction temperature and time, pH value and surfactant on phase composition and microstructure has been researched, and the best preparing technical parameters were obtained. Single-phase Bi2Se3 nanoplates have been synthesized in the NH3·H2O-NH4Cl buffer solution (pH=10),using of Bi(NO3)3·5H2O and Na2SeSO3 as starting materials, and EDTA was employed as complexing agent. The temperature of the solution was kept at 85℃for 6h. Uniform ultra-thin hexagonal nanoplates with the thickness of 20 nm and the edge length of 200nm were obtained. The mechanism of chemical synthesis of Bi2Se3 was assumed to be a ion reaction mechanisms, and the crystal growth mechanism was also researched. In the solution, based on the oriented attachment mechanism Se2- adsorption in Bi[EDTA]+surface, then heterogeneous nucleation, eventually grow into a hexagonal single crystal nanoplate. The maximum figure of merit ZT reaches 0.3 at 475 K, which is similar to Bi2Se3 bulk material prepared by solvo-thermal method.
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