论文总字数：30737字

摘 要

高性能环境友好型热电材料的开发是热电变换技术的重要环节。“高度结晶、高度织构、纳米化”的新思路是提高层状结构热电材料性能的重要策略。层状Na_xCoO₂具有极高的a-b面内电输运性能（电导率高、塞贝克系数大、功率因子高），同时该氧化物具有热稳定性好、毒性低、价格低廉等优点而受到热电学界的极大关注。但在多晶材料中，由于晶体取向高度无序造成电输运性能的下降；同时，其晶格热导率偏高。

本论文首先介绍了热电材料的研究背景及其基本原理，介绍了Na_xCoO₂的晶体结构、能带结构及Na_xCoO₂基热电材料的研究进展。讨论了Na_xCoO₂晶体的输运性能的各向异性，以及多晶块体中的晶粒织构度对输运性能的重要影响。在此基础上，本论文着重论述了层状材料高织构多晶块体的制备方法和影响因素，并讨论了一种基于高速液相辅助剪切和压力辅助放电等离子烧结工艺的新方法。针对Na_xCoO₂的结构特点，讨论了该方法的可行性和优点。

本课题拟通过高速液相辅助剪切手段对Na_xCoO₂微米级粉体实施粉碎，在细化颗粒度同时实现层状结构解理和颗粒径厚比提高，并压力辅助等离子烧结过程中获得高度织构的、纳米或纳-微米粒度的致密烧结体，以期提高其垂直于压力方向的电输运能力、降低晶格热导率，进而获得ZT值的有效提升。

关键词：Na_xCoO₂ 热电材料 高速液相辅助剪切 ZT值 织构

Effect of Liquid-based Shear Powder Treatment on the Microstructure and Thermoelectric Properties of Na_xCoO₂ Ceramics

Abstract

The development of high-performance environment-friendly thermoelectric (TE) materials is an important mission in TE conversion technology. The new strategy of high-crystalline, high-texturing and nanostructuring has been put forward for enhancing the properties of layered TE materials. Layered Na_xCoO₂ has extremely high a-b in-plane electrical transport performance (high conductivity, large Seebeck coefficient and high power factor). At the same time, the oxide Na_xCoO₂ has attracted great attention in thermoelectric field due to its advantages of good thermal stability, low toxicity and low price. However, in poly-crystalline materials, the high disorder of crystal orientation leads to the decrease of electric transport performance. At the same time, its lattice thermal conductivity is relatively high.

In this work, the research background, the basic principles of TE materials were introduced, and the crystal structure and band structure for Na_xCoO₂, a promising TE oxide, and the advances of Na_xCoO₂-based of materials were described as the emphasis. The anisotropy related to the special crystal structure of Na_xCoO₂, and, in return, the significance of micro-structural texturing was discussed in particular for enhancing the TE performance of layered compounds. Furthermore, the techniques for fabricating high-texture poly-crystalline bulks were reviewed. Based on our recent researches, a novel method employing a liquid-based shearing pulverization and a press-aided spark plasma sintering was described in particular, from the viewpoints of feasibility and advantages for Na_xCoO₂-based TE materials.

In this project, Na_xCoO₂ micron powder is to be pulverized by high-speed liquid-phase assisted shearing. While refine that granularity, cleavage of the layered structure and improvement of the particle diameter-thickness ratio are realize; In addition, highly textured compact sintered bodies with nano or nano-micron particle sizes can be obtained in the pressure-assisted plasma sintering process, so as to improve the electric transport capability perpendicular to the pressure direction, reduce the lattice thermal conductivity, and further effectively improve ZT value.

Key words: Na_xCoO_2; thermoelectric materials; liquid-based shear pulverization; ZT value; texture

目录

摘 要 I

ABSTRACT i

第一章 绪论 1

1.1 研究背景 1

1.2 热电材料 1

1.2.1热电材料的发展及研究现状 1

1.2.2 热电效应 2

1.2.3 热电材料评估参数 3

1.3 Na_xCoO₂的材料特点与研究进展 4

1.3.1 Na_xCoO₂的晶体结构 4

1.3.2 Na_xCoO₂的能带结构 5

1.3.3 Na_xCoO₂的研究进展及挑战 5

1.4 本课题的创新点与前景 6

1.5 织构 7

1.5.1提高织构的意义 7

1.5.2 织构方法 7

1.6 本课题的方法和研究内容 12

1.6.1 液相辅助剪切剥离法 12

1.6.2 放电等离子烧结法 13

1.6.3 本课题的研究内容 14

1.7 Na_xCoO₂的可行性与优势 14

1.7.1 Na_xCoO₂的可行性 14

1.7.2 Na_xCoO₂的优势 15

第二章 实验部分 16

2.1 实验流程 16

2.2 实验原料 16

2.3 实验仪器与设备 16

2.4 样品制备 16

2.5 分析与表征 17

第三章 分析与讨论 18

3.1 XRD分析 18

3.2 显微结构分析 19

3.3 电学性能 20

3.3.1 电导率σ 20

3.3.2 塞贝克系数S 20

3.3.3 功率因子PF 20

3.5 热电优值ZT 21

第四章 结果与展望 22

4.1 结果 22

4.2 展望 22

参考文献 23

致谢 28

1. 绪论
   1. 研究背景

随着人们环保意识的不断提高，为了解决能源紧缺，环境污染等问题，热电材料作为一种相对环保的功能材料，也受到了越来越多人的关注与重视。热电材料是一种能够实现热能和电能之间相互转换的功能材料，其核心热电转换装置不仅不污染环境，满足了人们对环保的要求，而且能够利用工业余热、废热和可再生能源进行温差发电，成本低，效率高，具有良好的综合社会经济效益。

热电材料是一种能够实现热能与电能之间相互转换的功能材料。热电现象从发现至今已经有很多年了，然而却一直没有实现真正意义上的运用于生活。直到20世纪50年代，热电现象才从真正意义上发展为一种有使用意义的能量转换技术与装置。随着微电子技术、超导技术等高新技术的发展，热电材料也得到了越来越多的实际应用。而随着能源与环境危机的加剧，适应21世纪绿色环保主题的具有体积小、重量轻、无传动部件、无噪声运行、精确可靠等优点的热电材料引起了材料研究学者的广泛重视。

• 1. 热电材料

1.2.1热电材料的发展及研究现状

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