氧化钛基半导体热电材料的研究进展

热电材料—即实现热能和电能之间直接相互转换的一类功能材料，提供了一种制冷或发电的新方法—在解决能源和环境危机问题上正在扮演越来越重要的角色。传统的三维材料中，由于几个决定热电性能的关键物理参数相互关联，使得现有热电材料很难获得较高热电优值（ZT）。金属氧化物热电材料由于其良好的耐高温性能，是中高温区使用的理想候选者。如果能提高氧化钛基化合物的热电优值，那么氧化钛基化合物将是一类非常优秀的热电材料，因为其不仅具有优良的化学稳定性和热稳定性，而且原材料丰富、不含有毒元素以及制备工艺简单。纳米化能显著降低材料的热导率，是最近二十年提高热电性能的一条主要途径。同时，通过界面和化学组成调控增加与电学性能相关的功率因子也是一种继续提高热电性能的重要方法。本文综述了我们近期对氧化钛基热电材料的研究成果，包括对钛酸盐纳米管较大赛贝克（Seebeck）系数的实验发现，提出利用一维纳米材料独特的空心结构和纳米管层状特殊构造，将两个相关联的物理参数（热导率和电导率）分别调控；通过合成氧化钛基纳米复合材料，研究界面对载流子和声子散射的作用，提出通过载流子能量过滤效应提高其热电性能；采用尿素燃烧法和高温烧结等方法合成具有纳米结构和化学组成调控的氧化钛基化合物，认识化学组成以及界面对声电输运的作用规律；最后介绍能显著提高热电材料功率因子的载流子非对称迁移的理论。

Research and Development of Titania-Based Nanostructured Materials for High Performance Thermoelectric Applications

Thermoelectric materials, which can convert heat directly into electricity efficiently and vice versa, offer a new method to refrigeration and power generation. They therefore play an important role on solving intensified energy crisis and environmental problems. In traditional bulk thermoelectric materials, it is difficult to further improve their figure of merit (ZT) because of strong correlation between the physical parameters which determine the thermoelectric performance. Thermoelectric metal oxides are ideal candidates which can be used at middle and high temperatures, due to their good thermal stability. If the thermoelectric properties of titania-based materials can be improved, it would make an excellent thermoelectric material owing to its non-toxicity, good chemical and thermal stability, natural abundance, and simple preparation process. Nanotechnology provides a dominant approach to improve the thermoelectric properties in the last twenty years, resulting from its remarkable effect to decrease the thermal conductivity. Meanwhile, to enhance the electron-related power factor by tuning the interface and chemical composition is also an important method to further increase the thermoelectric properties. In this paper, we reviewed our recent research results on titania-based thermoelectric materials. Firstly, through the experimental observation of large Seebeck coefficient of titanate nanotubes, we considered that the two correlated parameters, namely electrical conductivity and thermal conductivity,can be tailored separately by using the peculiar tube morphology and layer structure of one-dimensional materials; Secondly, by studying the different scattering effect of carriers and phonons at the interface by synthesizing titania-based nanocomposites, we proposed to enhance the thermoelectric properties by designing electron energy filtering; Thirdly, we found that nanostructured and chemically tuned titania-based materials could be prepared by using chemical methods such as urea combustion and high-temperature sintering and thus would help us to cognize the transport response of electron and phonon to chemical composition and interface. Finally, the asymmetrical carrier transport theory was introduced, which possibly provided an important way to notably enhance the power factor of thermoelectric materials.