Solvothermal Synthesis Of Sb₂Te₃-based Thermoelectric Material

â…¤-â…¥compound A₂B₃ are of good thermoelectric properties, which can be widely used in the cooling devices and power generators. Recently, Bi₂Te₃,Sb₂Te₃,Sb₂Se₃ as well as solid solution alloy have been investigated domestically and abroad. It's the mature and high-property thermoelectric materials recently, which are in applications near room temperature, however, the ZT merit of these materials has been close to 1 more or less. The figure of merit of TE materials could be significantly improved if the materials were nano-structured, since the thermal conductivity could be decreased more significantly than the decrease of the electric conductivity of the materials.In the thesis, solvothermal synthesis has been explored to prepare Sb₂Te₃ as well as Sb₂Te₃-based solid solution material. The initial raw materials are listed as follow: SbCl₃,BiCl₃,Te powder and Complexing agent of EDTA. Nano-structured Sb₂Te₃ powders have been yielded through different synthesis conditions. The structure and morphologies of nano-powders were investigated by XRD, SEM, TEM and EDS observations. The growth mechanism of Sb₂Te₃ crystal as well as Sb2Te3-based solid solution have been researched. The development of the synthesis of Sb₂Te₃ is shown in the following paragraphs.The Sb₂Te₃ nano-powder with the particle size of 100～600nm has been prepared by solvothermal synthesis. The effect of reaction temperature and time on the phase composition and mirco-structure have also been studied. The results indicate that the particle size of the powders significantly increase with the escalated temperature. When the temperature reaches 180 degree, there has been no impact of the reaction time on the phase structure of the powders, however, the particle sizes increase with the prolonged time. At the temperature of 180 degree and maintaining for 24 hours, Sb₂Te₃ powder of hexagonal crystal was yielded. The average grain size was approximately around 200 nm.In order to obtain the structure-controlling Sb₂Te₃ nano-powder, with the additive of EDTA, various morphologies of Sb₂Te₃ have been synthesized by solvothermal process. It is mainly investigated that the mount of additive EDTA impact on the product component and the mirco-structure. Results show that when Sb³⁺: EDTA=1 : 1, the morphologies of the as-synthesized powder are largely hexagonal crystals, as well as a minority of polygonal crystal (octahedron). When Sb³⁺: EDTA=2 : 1, the morphologies of the as-synthesized powder are largely polygonal crystal (octahedron), as well as a minority of hexagonal crystals. The nucleation and growth of Sb₂Te₃ nanocrystals has been discussed.Aimed to adjust the carrier concentration of the Sb₂Te₃, and then optimize the electrical properties, we have successfully fabricated the (100-x) mol%Sb₂Te₃ + xmol%Bi₂Te₃ solid solution. Through analyzing the XRD of the solid solution, we discover that the high-angle peaks obviously shift toward the low-angle. Therefore, the lattice constants increase as the x increase. The mircro-structure has been characterized by SEM,TEM and EDS. The outcome revealed the particle size is apt to decrease with the increasing x figure. At the temperature of 180 degree and maintaining for 12 hours, BiSbTe₃ nano-powder was yielded. The average grain size was approximately around 100 nm.Finally, the nucleation and growth of Sb₂Te₃ nanocrystals have been investigated, and also the mechanism of "surface-nucleation lateral growth" were proposed.