【作者】 张帆；

【导师】 周健；

【作者基本信息】 南京大学 ， 材料工程（专业学位）， 2016， 硕士

【摘要】 近年来,随着工业的快速发展,能源供应日益短缺,环境友好的可再生能源技术成为人们研究的关注重点,其中热电转化技术是人们研究的重点之一。热电技术的研究主要集中在开发新的热电材料以及如何对现有的热电材料进行改性。本论文拟以目前受到研究工作者广泛关注的层状热电材料为研究对象,主要包括BiCuXO (X= Se, Te)基和Bi2Sr2Co2Oy基两类层状氧化物热电材料。采用复合的方法来优化这两类材料的电导率或者热导率,并进一步研究复合对其热电性能的影响。主要研究工作如下：1> BiCuTeO与BiCuSeO复合对热电性质影响的研究通过对比球磨前后BiCuSeO和BiCuTeO陶瓷的电输运结果,发现球磨可以提高陶瓷样品的电导率。经过球磨成功制备了结构稳定成分均匀的(1-x)BiCuSeO+xBiCuTeO复合陶瓷,对其热电性质进行研究发现,随着体系中BiCuTeO成分的增多,样品的电导率有了很大的提高,这是因为BiCuSeO电导率比较低而BiCuTeO电导率比较高,从而提高了体系的电导率,使得0.9BiCuSeO+0.1BiCuTeO的样品ZT值与BiCuSeO相比有了很大的提升。但是由于BiCuTeO的Seebeck系数较低,所以0.1BiCuSeO+0.9BiCuTeO的样品ZT值与BiCuSeO相比变化不大。2、Bi2Sr2Co2Oy复合碳对热电性质影响的研究采用光学浮区法生长了结构稳定成分均匀的(1-x)Bi2Sr2Co2Oy+xC复合单晶体系,对其热输运性质进行研究发现,分别复合碳纳米管和多孔碳后,样品的热导率都有所降低,这是因为碳材料的结构疏松多孔,晶体结构空隙大,提高了晶格声子散射的能力,从而降低了晶格热导率。但是对该体系的电输运性质进行研究发现,复合碳材料后,电导率也降低了几个数量级,这是因为碳纳米管和多孔碳的导电性都不好,降低了载流子迁移率导致的。通过上述研究,我们对层状结构的BiCuXO (X=Se, Te)和Bi2Sr2Co2Oy体系的微结构、电输运和热输运有了更深的理解。对于BiCuXO (X=Se, Te)体系,通过复合的方法可以提高热电性能,但复合的时候量要适度,把握好电导率和Seebeck系数的平衡是关键问题。应多次尝试改变复合的量,找到一个最佳组合点使功率因子达到最大,从而最大程度地提升材料的热电性能。对于(1-x)Bi2Sr2Co20y+xC体系,应选择复合烯化碳材料,由于这一类材料的导电性很好,能够实现降低热导率的同时提高电导率,提升Bi2Sr2Co2Oy基材料的热电性能。更多还原

【Abstract】 Since the industrial revolution, because of the rapid development of human society, demand for energy is increasing, while the rapid development of the industry also makes the increasingly serious environmental pollution. Thus, environmentally friendly renewable energy technologies become concerned about the hot research, among which thermoelectric conversion technology is highly expected. The investigation of thermoelectric materials focus on new thermoelectric materials and how to improve ZT base on some potential thermoelectric materials. Composite is also an effective path for improving thermoelectric property. Subject of the present paper is several layered oxide thermoelectric materials, including BiCuXO (X= Se, Te) and Bi2Sr2Co2Oy materials systems. The ZT values of the two thermoelectric materials are not high because it’s restricted by their thermoelectric parameters. Wherein due to the low electrical conductivity of BiCuSeO, resulting in poor thermoelectric performance, and the high thermal conductivity of Bi2Sr2Co2Oy, we use compositing methods to optimize the electrical conductivity or thermal conductivity of these two materials, and study their thermoelectric performance. The main research works are described as follows:1. thermoelectric properties of BiCuTeO and BiCuSeO compositeWe compare the electrical transport properties of BiCuXO (X=Se, Te) ceramics before and after ball-milling, showing ball-milling can improve the electrical conductivity of the ceramic samples. The study of (1-x)BiCuSeO+xBiCuTeO composite ceramics shows, with the increase of BiCuTeO component, the electrical conductivity of the sample has been greatly improved, which is because BiCuTeO’s conductivity is relatively high, reasulting in increasing carrier concentration, thereby increasing the conductivity, so the ZT value of 0.9BiCuSeO+0.1BiCuTeO has been greatly improved compared with BiCuSeO. However, due to the low Seebeck coefficient of BiCuTeO, the ZT value of 0.1BiCuSeO+0.9BiCuTeO changed little compared with BiCuSeO.2. thermoelectric properties of Bi2Sr2Co2Oy and carbon composite(1-x)Bi2Sr2Co2Oy+xC single crystals are grown through optical floating zone method. The study shows, after compositing carbon nanotubes and porous carbon, the thermal conductivity of both composites are reduced. This is because carbon materials have large gaps, enabling atomics to vibrate in the gaps, resulting in improving the ability of the lattice phonon scattering, thereby reducing the lattice thermal conductivity. However, the electrical conductivity is reduced by several orders of magnitude, because the electrical conductivity of carbon nanotubes and porous carbon are pretty low, leading to reduce the carrier mobility.Through these studies, we have a better understanding of BiCuXO (X= Se, Te) and Bi2Sr2Co2Oy materials systems. For BiCuXO (X= Se, Te) system, the thermoelectric performance can be improved through compositing, but the amount of compotents should be appropriate. The key issue is to grasp the balance of electrical conductivity and Seebeck coefficient. We could change several times the amount of compotents, so we can find the best combination to maximize the power factor. For (1-x)Bi2Sr2Co2Oy+xC system, we could composite alkylene carbon materials. Because the electrical conductivity of this kind of materials is very good, the thermal conductivity can be reduced while improving the electrical conductivity, thereby the thermoelectric properties of Bi2Sr2Co2Oy system is improved.更多还原