电沉积Bi-Te薄膜的形貌结构与性能表征

发布时间：2018-06-01 05:34

本文选题：电化学沉积 + 碲化铋　；参考：《北京化工大学》2015年硕士论文

【摘要】：热电材料是一类性能优越的功能材料,它能把热能和电能直接转换,对它的研究也日益受到重视。Bi-Te基化合物是已知的室温下性能最好的热电材料,通过低维化和合适的掺杂改性能进一步提高材料的热电性能。本研究通过成本低廉、工艺简单、可宏量制备的电沉积方法在铜基底上制备了理想化学计量比的Bi2Te3纳米热电薄膜,探索了薄膜的电沉积工艺和析出机制,重点研究了表面活性剂溴化十六烷基三甲铵(CTAB)和第三掺杂组元Cu的加入对薄膜形貌结构组成与热电性能的影响。通过调节沉积电位、沉积时间、电解液浓度可实现对Bi2Te3薄膜形貌、结构、成分的精准控制,在-0.1V (vs.SCE),30min,7.5mM Bi3+和10mM HTeO2+条件下可以制得形貌良好、结构均一并且具有理想化学计量比(Bi：Te=2：3)的热电薄膜。此外本课题还深入探索Bi2 Te3纳米热电薄膜的析出机制,结果表明,Bi2Te3薄膜析出反应是分步进行的：Bi3+先得一部分电子生成中间价态的Bix+,随后Bix+被还原得到Bi单质；同时HTeO2+先吸附在基底表面,得一部分电子生成Tex+,Tex+再被还原得到Te单质；最后单质Bi和单质Te结合生成Bi2Te3薄膜。本课题将CTAB作为一种特殊的添加剂应用于改善电沉积法制备Bi2Te3热电薄膜。X射线衍射、电子能谱、扫描电子显微镜的分析结果表明,在100mg·L-1 CTAB、7.5mM Bi3+、10mM HTeO2+和1mM HNO3的电解液浓度条件下,能制备出多孔片层状并具有(110)晶面择优取向的热电薄膜。热电性能的测试结果表明CTAB的加入能使薄膜的电阻率降低5倍左右,塞贝克系数和功率因子也得到提高,薄膜的热电性能明显优化。而电化学分析结果表明,电沉积过程时CTAB的极性部分会吸附在铜基底或者已形成的Bi2Te3颗粒表面而改变颗粒晶面的表面能,使得Bi、Te的沉积电位都发生了负移。这种作用使得薄膜不再单一地垂直堆叠生长,而是呈球状颗粒均匀生长。本研究还将Cu作为第三掺杂元素制备了化学计量比组成为CuxBi2Te3的三元热电温差薄膜,并就Cu源掺杂浓度对薄膜形貌结构组成的影响进行了研究。结果表明,Cu源的引入可以使形成薄膜的片层变薄,提升颗粒间致密性,并使材料的电阻率明显下降,塞贝克系数和功率因子显著升高,有效提升了其热电性能。
[Abstract]:Thermoelectric materials are a kind of functional materials with superior performance. They can convert heat energy and electric energy directly. The study of thermoelectric materials has been paid more and more attention to. Bi-Te based compounds are known to be the best thermoelectric materials at room temperature. The thermoelectric properties of the materials can be further improved by low dimensional and appropriate doping modification. In this study, the Bi2Te3 nano-thermoelectric thin films with ideal stoichiometric ratio were prepared on copper substrates by electrodeposition method with low cost, simple process and macroscopical preparation, and the electrodeposition process and precipitation mechanism of the films were explored. The effects of cetyltrimethylammonium bromide (CTAB) and the third doped component Cu on the morphology and thermoelectric properties of the films were studied. By adjusting the deposition potential, deposition time and electrolyte concentration, the morphology, structure and composition of Bi2Te3 thin films can be precisely controlled. The morphology of Bi2Te3 films can be obtained under the conditions of -0.1V / v / s. A homogeneous thermoelectric film with an ideal stoichiometric ratio of 2: 2: 3). In addition, the precipitation mechanism of Bi2 Te3 nano-thermoelectric thin films is also explored. The results show that the precipitation reaction of Bi2Te3 thin films is a step by step reaction: first, a portion of electrons are obtained to form intermediate valence Bix, and then Bix is reduced to Bi simple mass. At the same time, HTeO2 is first adsorbed on the substrate surface, and some electrons are generated by Tex Tex and then reduced to Te. Finally, Bi and Te are combined to form Bi2Te3 thin films. In this paper, CTAB was used as a special additive to improve the electrodeposition of Bi2Te3 thermoelectric thin films. The results of X-ray diffraction, electron spectroscopy and scanning electron microscopy showed that under the conditions of 100mg L-1 CTAB 7.5mm Bi3 Bi3 10mm HTeO2 and 1mM HNO3 electrolyte concentration, The thermoelectric thin films with layered porous sheet and preferred orientation of crystal plane (110) can be prepared. The test results of thermoelectric properties show that the resistivity of the films can be reduced by about 5 times with the addition of CTAB, and the Seebeck coefficient and power factor are also improved. The thermoelectric properties of the films are obviously optimized. The results of electrochemical analysis show that the polar part of CTAB is adsorbed on the copper substrate or on the surface of formed Bi2Te3 particles during electrodeposition, and the surface energy of the grain surface changes, which results in the negative shift of the deposition potential of CTAB. Because of this effect, the thin films are grown as spherical particles instead of single vertical stacking. The ternary thermoelectric thin films with stoichiometric ratio of CuxBi2Te3 were prepared by using Cu as the third doped element, and the effect of Cu source doping concentration on the morphology and structure of the films was studied. The results show that the introduction of Cu source can thin the lamellar layer and improve the intergranular compactness, and the resistivity of the material decreases obviously, the Seebeck coefficient and power factor increase significantly, and the thermoelectric properties of the film are improved effectively.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34;TQ153

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