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Solvothermal Synthesis of Nanostructured Rare-earth Substituting Bi2Te3 Based Thermoelectric Materials

Author: ZhangYanHua
Tutor: ZhaoXinBing
School: Zhejiang University
Course: Materials Science
Keywords: Thermoelectric materials Solvothermal / hydrothermal synthesis method Bi2Te3 Rare Earth Elements Nanostructures Crystal structure Nucleation and growth mechanisms Thermoelectric properties
CLC: TB383.1
Type: Master's thesis
Year: 2005
Downloads: 264
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Abstract


Thermoelectric materials is a way to achieve the direct conversion of heat and electricity Functional Materials, has important application value and wide application prospect in the field of thermoelectric power generation and thermoelectric cooling. The Bi 2 Te 3 Compounds highest dimensionless figure of merit ZT close to 1, is the best thermoelectric materials near room temperature applications. Preparation of Nano and low-dimensional thermoelectric materials help improve the thermoelectric properties of the material. By solvothermal / hydrothermal synthesis method, to BiCl3, Te powder or Te compounds, as well as the rare earth compound as the precursor, using different synthesis route, synthesized a variety of rare earth element-containing BI 2 the Te 3 -based alloy nano-powder and Bi 2 Te 3 nano powder, the XRD, TEM, SEM and other means of synthetic powder object analysis of the phase composition and morphology of the structure; experimental research and Bi 2 Te 3 hydrothermal synthesis process, the chemical reaction mechanism and nucleation growth mechanism are discussed in detail. Technology finally by vacuum hot pressing, hot pressing the partial of Bi 2 Te 3 -based alloy nano powders, and test its thermoelectric properties. This paper mainly achieved the following results. A particle size of about 30nm LaxBi 2 Te3 x (x ≤ 1) thermoelectric materials nano powder. Solvothermal synthetic method. And to study the influence of the reaction temperature and reaction time on the product composition and microstructure, studies have shown that, with rare earth element La Bi 2 Te 3 compounds with standard Bi 2 Te 3 has a similar crystal structure and lattice constant of the crystal phase of La content is significantly improved with increasing the synthesis temperature, and the reaction time on the La x the Bi 4 Te 6 La content had no significant effect, and the initial judge La of Bi , Te , 2 3 phase occupy the position of the Bi atoms in the crystal lattice. Bi , Te 2 3 -based compounds layered crystal structure, the geometry of the synthetic product ion diffusion speed and crystal growth temperature. Product synthesized at the lower temperature to the irregular polyhedron nanoparticles mainly the increasing temperature synthesis product morphology curved flaky, and there is a small amount of nano-tubes. 2 using a hydrothermal synthesis method, adds a proper content EDTA and strong alkaline conditions (adding NaOH) was prepared the La x of Bi 2 the -x the Se y Te 3 the , y quaternary alloy, and major research synthesis Cheng Zhongqiang alkaline conditions and the addition of EDTA on the reaction products impact studies have shown that adding a sufficient amount of basic additive synthesis of single-phase Bi 2 Te 3 -based alloys necessary condition; Add appropriate amount of EDTA makes the solution nanosheets \self-assembly connected to form a nano-crystal lamellae arranged parallel to each unique petal-like organization. However, the addition of excess EDTA will inhibit the synthesis reaction to form a granular Bi, and rod TeSe solid solution. 3 by hydrothermal method, were synthesized containing rare earth elements La Bi 2 the Te 3 -based ternary alloys and quaternary alloys (Also doped Se) compounds were prepared. And to study the temperature dependence of the crystal structure characteristic of the product and the thermoelectric performance parameters. The study found that, of Bi 2 the Te 3 the base ternary or quaternary alloy crystal structure with standard's of Bi of 2 the Te 3 basically similar, are hexahedral layered structure of rare earth elements La placeholder in the unit cell is randomly replaced the Bi 2 Te 3 lattice 6c Bi atoms, quaternary alloy the Se atoms replace most of 3a and a small part 6c Te atoms. Calculation accounted median actual composition of its synthetic product that basically consistent with the design content. Bi 2 the Te 3 -based ternary or quaternary alloy specimens thermoelectric performance analysis, Bi 2 Te 3 < / sub>-based ternary and quaternary alloys thermoelectric materials are n-type semiconductor, indicating replacement Bi

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