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1、 毕 业 论 文 论文题目 两类过渡金属化合物热电材料的生长及 输运性质研究 学 科 、专 业 名 称 凝聚态物理 研 究 方 向 热电材料的生长与输运性质研究 摘要摘要自19世纪工业革命以来，在全世界范围内，人类对能源的需求快速增长。为了满足工业生产和日常生活的能源需求，不可再生能源（如煤炭、石油、天然气等化石燃料）被大量开采及使用，这些能源的使用造成了严重的环境污染问题，比如空气污染、温室效应、酸雨等。而我国的能源形势更不容乐观，其最主要的原因在于能源需求量巨大和能源利用效率低下。具体而言，从2007年起我国是全世界第二大能源生产国和消费国，二氧化碳的排放量位居全球第二位。而且我国的能源结
2、构十分不合理，能源利用效率低下，造成了严重的能源浪费现象，从而对环境产生了严重的污染与破坏。在我国的工业用能中，大约60%的能源转化为工业废热资源，且工业废热利用率低下（仅为30%）。所以为了减少能源消耗和降低环境污染，我国亟需提高工业废热的利用率。在这种背景下，热电材料走进了人们的视野，引起了人们的广泛关注，因为热电效应使热能和电能可以直接转换，可以对工业废热加以利用。热电材料是一种环境友好型的热能-电能转换材料，具有体积小、可靠性高、无污染、温度适用范围广等优点。由于目前热电设备的效率不够高，所以需要对热电材料的电输运和热输运性质进行系统研究，以提高热电材料的热电性能。推动热电材料在工业生
3、产和日常生活中的实际应用，达到提高废热利用率、节约能源和保护环境的终极目的。本文通过不同的生长方法制备了一系列热电材料单晶和多晶陶瓷样品，利用物理性质综合测量系统研究了二类热电材料单晶和多晶陶瓷样品的电输运和热输运性质。主要结论如下：1. 通过化学气相输运法和高温固相合成法，分别生长制备获得Te缺的ZrTe5-d单晶及富Te的ZrTe5+d多晶陶瓷，通过综合物性测量系统分别对Te缺的ZrTe5-d单晶及富Te的ZrTe5+d陶瓷的电输运性质和热电性质进行了研究与比较。发现通过对Te元素化学计量的控制，改变了ZrTe5化合物的电输运性质，从而达到调控ZrTe5化合物热电参数和提高ZrTe5化合物
4、热电性能的目的。具体而言富Te的ZrTe5+d陶瓷在室温300K时电阻率、Seebeck系数、热导率和热电优值ZT分别为6.0 mWcm、123 VK-1 、1.86 W/(mK)和0.037。ZT值在过去文献中报道的ZrTe5/HfTe5中最高。这一工作为进一步提升热电材料性能提供了思路。2. 通过化学气相输运法和高温固相合成法，分别生长制备获得BiCuSO单晶、BiCuSeO单晶和BiCuTeO多晶陶瓷，通过综合物性测量系统分别对这些样品的电输运性质进行了研究与比较；对BiCuXO (X=S,Se,Te)材料的电子散射机制有了较深入的研究，发现元素替换(从S到Te)显著减小了BiCuXO材
5、料体系电阻率。并且从BiCuSeO到BiCuTeO，电声子耦合作用对载流子的散射逐渐减小。总结ZrTe5和BiCuXO (X=S,Se,Te)材料这两个体系的实验结果与理论分析我们发现：对元素化学计量的控制和元素的替换可以实现对材料电输运性质的有效调控。因此，我们可以基于以上方法，调控热电材料的电输运性质从而提升热电材料的热电性能。电子散射机制的研究有可能提供改善热电材料系统电导率的新思路。关键词：ZrTe5；BiCuXO；晶体生长；化学气相输运法；电输运；热电性质IIAbstractAbstractSince the Industrial Revolution of the 19th cen
6、tury, the demand for energy has grown rapidly all over the world. In order to meet the energy demand of industrial production and daily life, non-renewable energy(such as coal, oil, natural gas and other fossil fuels) has been extensively exploited and used, resulting in serious environmental pollut
7、ion problems, such as air pollution, greenhouse effect, acid rain and so on. Compared with other countries, energy situation of China is not optimistic, because of the large demand for energy and the the inefficient use of energy. China has been the second largest energy producer and consumer in the
8、 world since 2007. Carbon dioxide emissions are the second largest in the world. Due to the non-optimized energy usage structure and the energy use inefficiency, China has caused serious energy waste, which has caused serious pollution and environmental problems. In China, about 60% of industrial en
9、ergy is converted into industrial waste heat, and the utilization rate of industrial waste heat is as low as 30%. Therefore, in order to reduce energy waste and environmental pollution, it is urgent for China to increase the utilization rate of industrial waste heat.In this background, thermoelectri
10、c materials have come into peoples vision and attracted intensive attention, because the thermoelectric effect enables the direct conversion of heat to electrical energy, and can be used to take advantage of industrial waste heat. Thermoelectric material is an environment-friendly heat-electrical-en
11、ergy conversion material, which has the advantages of small size, high reliability, pollution-free, wide temperature application range and so on. At present, the efficiency of thermoelectric devices are still not high enough, so it is necessary to study the electrical and thermal transport propertie
12、s of thermoelectric materials to improve their thermoelectric performance, promote the practical utilization of thermoelectric materials in industrial production and daily life to achieve the ultimate goal of improving the utilization rate of waste heat, conserving energy and protecting the environm
13、ent.In this paper, a series of single crystal and polycrystalline ceramics samples of thermoelectric materials have been prepared by different methods. The electrical and thermal transport properties of these materials have been measured by Physical Property Measurement System. The main conclusions
14、are:1. Te-deficient ZrTe5-d single crystal and Te-rich ZrTe5+d polycrystalline ceramics were grown by chemical vapor transport method and high temperature solid-state reaction method respectively. The electrical and thermal properties of Te-deficient ZrTe5-d single crystal and Te-rich ZrTe5+d polycr
15、ystalline ceramics were studied and compared by Physical Property Measurement System characterizations. It is found that the electrical transport properties of ZrTe5 compounds are changed by controlling the stoichiometry of Te elements so that the thermoelectric parameters of ZrTe5 compounds can be
16、adjusted and the thermoelectric properties of ZrTe5 compounds can be improved. In details, the electrical resistivity, Seebeck coefficient, thermo-conductivity and ZT value of ZrTe5+d ceramics are 6.0 mW cm、123 VK-1 、1.86 W/(mK) and 0.037 measured at 300 K, respectively. ZT value of our sample is higher
