摘要
热电材料是一种能将热能和电能直接转换的功能材料,在温差电致冷和温差发电方面具有重要的应用前景。传统Bi_2Te_3基合金热电优值ZT在1左右,是目前室温附近性能较好的热电材料。而近年来不少学者把目光转向了性能更好的Bi_2Te_3-Sb_2Te_3基纳米复合热电材料以及Sb_2Te_3单相合金。本文先采用一步水(溶剂)热法合成出Bi_2Te_3及Sb_2Te_3单相,然后在三元合金复合材料的研究中,尝试了Sb_2Te_3-Bi_2Te_3基材料的二次(两步)水热法合成实验;采用一步混合水热法制备出BixSb2-xTe3三元合金;通过物理混合法制备Bi_2Te_3/ Sb_2Te_3三元复合材料并测试了其电性能。
以N2H4·H2O为还原剂分别在水热条件与溶剂热(乙醇)条件下合成出了Bi_2Te_3单相粉体。SEM分析表明后者环境下的产物更均匀,但尺寸颗粒相对较大。电性能测试表明合成的样品均为n型半导体,虽然后者环境下样品的电导率不到前者的1/8,但Seebeck系数比前者明显高出许多,达到-98μV/K,这主要由于样品的微观形态与杂质Te的含量不同所引起。
240℃,48h水热条件下合成出了纯相的Sb_2Te_3六角片。研究表明反应时间,碱浓度直接影响着Sb_2Te_3的纯度其次是形貌;温度对Sb_2Te_3六角晶片的厚度有着重要影响;不同的Te源会导致Sb_2Te_3晶片形态、尺寸的变化,主要是由于形核机理的不同而导致晶核数量上的差异所引起;表面活性剂EDTA-2Na使晶体变得更宽大主要取决于自身与Sb3+的配位作用,而PVP通过改变水热环境导致产物中有大量的不规则Sb_2Te_3块状晶粒存在。
先以K(SbO)C4H4O6 ,Te粉为原料,N2H4·H2O为还原剂,水热合成出富Te的Sb_2Te_3+x前驱粉体,再以此为原料再加入Bi(NO3)3·5H2O等进行第二次水热合成,最终得到具有部分核壳结构的Sb_2Te_3-(Bi_2Te_3)x/3的纳米复合材料。XRD测试表明在第二步水热合成过程中过量的Te已经得了到最大程度的利用。SEM及EDAX分析表明Sb_2Te_3- (Bi_2Te_3) x/3已初步具有了部分的纳米核壳包覆结构。电性能测试表明正是这种不完全包覆界面的存在,使得该材料室温下的Seebeck系数较纯Sb_2Te_3提高了约60μV/K。
Thermoelecrtic (TE) materials are a kind of functional materials which can directly convert heat energy to electricity or reversely and it has an important application prospect in TE cooling and power generating.The traditional Bi_2Te_3 based materials, whose figure of merit ZT is about 1, are known as one of the best TE materials currently at room temperature unit now. With the Bi_2Te_3 based materials being researched more sophisticated, many scholars turned their eyes to Sb_2Te_3-Bi_2Te_3 nanocomposites and Sb_2Te_3 single phase. In this paper,firstly,Bi_2Te_3 and Sb_2Te_3 single phase was prepaired by one-step hydrothermal (solvothermal) synthesis respectively. Then in the studying ternary alloyed composites, we had a research on the double (two-step ) hydrothermal synthesis of Sb_2Te_3-Bi_2Te_3 based compounds;BixSb2-xTe3 ternary material was hydrothermally synthesized; Bi_2Te_3 / Sb_2Te_3 composites was prepared by physical mixed methods and test its electrical properties was tested.
Bi_2Te_3 nanopowders was hydrothermally and solvothermally(ethanol) synthesized respectively N2H4·H2O as reductive.The SEM images showed that the latter product more uniform, but at relatively larger size . Electrical property tests showed that the samples are both n-type semiconductors .Although the conductivity of the latter simple is very little,only 1 / 8 of the former, its Seebeck coefficient which reach about -98μV / K is obviously much higher than the former . This was mainly due to the different morphology of samples as well as different impurity content of Te .
Sb_2Te_3 hexagonal nanoplates was hydrothermally synthesized at 240℃in 48h. Study showed that the reaction time, alkali concentration directly impact on the purity and morphology images of Sb_2Te_3 and temperature impacts on the thickness of the Sb_2Te_3 hexagonal plates significantly. Different Te sources leading to the changes of Sb_2Te_3 plates in morphology and size, mainly due to the different nucleation mechanism which led to the difference in the number of Sb_2Te_3 nuclei. In addition, surfactants EDTA-2Na make Sb_2Te_3 crystal bigger and thiner depended primarily on its ligand-relationship with the Sb3+ then PVP caused a large number of irregular Sb_2Te_3 particles by changing the hydrothermal environment .
Precursor Sb_2Te_3+x powders was hydrothermally synthesized with Te powders and K(SbO)C4H4O6 as precursors, N2H4·H2O as reductive firstly.Then the second hydrothermal synthesis was operated with Sb_2Te_3+x ,Bi(NO3)3·5H2O, N2H4·H2O,KOH as materials so as to get the final product—Sb_2Te_3-(Bi_2Te_3) x nanocomposites with part-coated core-shell structure. XRD tests showed that in the second step hydrothermal synthesis process the excessive Te in Sb_2Te_3+x had been fully used. SEM and EDAX analysis showed that Sb_2Te_3-(Bi_2Te_3) x had formed part of core-shell structure initially which resulted Seebeck coefficient of the composites increased by 60μV / K than pure Sb_2Te_3 at room temperature.
引文
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