论文总字数：31816字

摘 要

热电材料是利用热电效应实现热能和电能直接转换的功能材料。热电效应之一的Seebeck效应是指将两种不同的金属或半导体接成闭合电路,把两个接点分别置于温度不同的两个环境中,电路中有电流产生。热电材料在温差发电和便携式制冷等方面有重要应用。提高热电材料的手段主要是协调优化电导率、Seebeck系数和热导率三个参数，从而提高热电转换效率。

本课题研究了不同的合成手段（如固相烧结法，SPS烧结法等）和过渡金属元素掺杂对ZnO的结构、热电性能的影响。使用固相烧结法和SPS法制备了ZnO样品，发现较高温度下两种制备方法合成的ZnO热电性能相差不大；用固相烧结法制备了Zn_1-xCo_xO（x=0、0.025、0.05、0.075、0.10）的单掺样品，发现Co掺杂会降低ZnO的电导率和热导率并提高Seebeck系数的绝对值，适当掺杂浓度的Co掺杂会带来ZT值的提高，x=0.025和x=0.075的Zn_1-xCo_xO样品在723K时ZT值均达到了0.017左右，相比于同样温度下未掺杂ZnO提高了70%左右；用固相烧结法制备了Zn_0.975-xCo_0.025Ni_xO（x=0、0.03、0.04）、Zn_0.975-xCo_0.025Cu_xO（x=0、0.03、0.04）的双掺样品，发现了过渡元素的双掺能够大幅降低ZnO的热导率，323K下x=0.04的Zn_0.975-xCo_0.025Cu_xO的热导率仅为1.3 W*m^-1*K^-1，相比同样温度下单掺Co样品的热导率下降了93.7%。

关键词：掺杂 电导率 热导率 Seebeck系数 ZnO

ABSTRACT

Thermoelectric materials are functional materials which use thermoelectric effect to realize direct conversion of heat to electricity. As one of the thermoelectric effects, Seebeck effect refers to the temperature gradient-induced voltage. It means when two different metals or semiconductors are connected in a closed circuit and their two contacts are placed in different temperatures, current will be produced. Thermoelectric materials have important applications in thermoelectric power generation and portable refrigeration. The main way to improve thermoelectric conversion efficiency is to coordinate and optimize the three parameters: electrical conductivity, Seebeck coefficient and thermal conductivity.

In this paper, the effects of different synthesis methods (such as conventional solid state sintering, SPS sintering, etc.) and transition metal doping on the structure and thermoelectric properties of ZnO were studied. Zinc oxide samples were prepared by conventional solid state sintering and SPS methods. It was found that the thermoelectric properties of zinc oxide synthesized by the two methods were similar at higher temperatures. Single-doped samples Zn_1-xCo_xO (x=0,0.025,0.05,0.075, 0.10) were prepared by conventional solid state sintering. It was found that the conductivity and thermal conductivity of zinc oxide were decreased and the absolute value of Seebeck coefficient was increased by Co doping with appropriate doping concentration. The ZT value of Zn_1-xCo_xO samples with x=0.025 and x=0.075 reached about 0.017 at 723K, which was about 70% higher than that of undoped ZnO samples at the same temperature. The co-doped samples Zn_0.975-xCo_0.025Ni_xO (x=0,0.03,0.04), Zn_0.975-xCo_0.025Cu_xO (x=0，0.03，0.04) were also prepared by conventional solid state sintering method. It was found that the co-doping of transition elements could significantly reduce the thermal conductivity of ZnO.The thermal conductivity of Zn_0.975-xCo_0.025Cu_xO when x=0.04 is only 1.3 W*m^-1*K^-1 under 323K, which is 93.7% lower than that of Co-doped samples at the same temperature.

KEY WORDS: doped, electrical conductivity, thermal conductivity, Seebeck coefficient, ZnO

目 录

摘 要 I

ABSTRACT II

第一章 绪论 1

1.1 热电效应及应用 1

1.1.1 热电效应原理 1

1.1.2 热电性能的表征 2

1.1.3 热电材料的关键问题和设计思路 3

1.1.4 热电材料的应用 3

1.2热电材料的分类及研究进展 4

1.2.1 传统热电材料 4

1.2.2 声子玻璃-电子晶体热电材料 6

1.2.3 低维热电材料 6

1.2.4 氧化物热电材料 6

1.3 ZnO热电材料 8

1.3.1 结构特性 8

1.3.2传统掺杂工艺 10

1.3.3研究现状 10

第二章 实验内容及方法 14

2.1 实验原料及设备 14

2.1.1 实验原料 14

2.1.2 实验设备 14

2.2元素添加方案 15

2.3 合成方法 15

2.3.1 固相烧结法 15

2.3.2 放电等离子烧结 16

2.4物相分析方案 16

2.5热电性能表征 16

2.5.1 Seebeck系数及电导率测量 16

2.5.2 热导率测量 17

第三章 制备方法对ZnO热电性能的影响 19

3.1 XRD物相分析 19

3.2 热电性能 19

3.2.1 电导率 19

3.2.2 Seebck系数 20

3.2.3 功率因子 21

3.2.4 热导率 22

3.2.5 ZT值 23

3.3 小结 23

第四章 Co掺杂对ZnO热电性能的影响 24

4.1 XRD物相分析 24

4.2 热电性能 25

4.2.1 电导率 25

4.2.2 Seebeck系数 26

4.2.3 功率因子 27

4.2.4 热导率 28

4.2.5 ZT值 29

4.3 小结 30

第五章 Ni、Co共掺对ZnO热电性能的影响 31

5.1 XRD物相分析 31

5.2 热电性能 32

5.2.1 电导率 32

5.2.2 Seebeck系数 32

5.2.3 功率因子 33

5.2.4 热导率 34

5.2.5 ZT值 35

5.3 小结 36

第六章 总结 37

参考文献 38

第一章 绪论

1.1 热电效应及应用

1.1.1 热电效应原理

热电效应是由温差引起的电效应和由电流引起的可逆热效应的总称｡1821年,Seebeck发现,将两种不同的金属导线首尾相连形成回路,如果把两个接点分别置于温度不同的两个环境中,则电路中有电流产生，即Seebeck效应，如图 1.1(a)所示。这种情况下产生电流的电动势叫做温差电动势｡1834 年,Peltier 发现 Seebeck 效应的逆效应,即当电流通过由两种不同金属而制成的回路时,除了产生焦耳热外,还在接点处发生与电流方向有关的热量的放出或吸收｡这种由于电流通过不同导体的接触点而发生放热或吸热的现象称为Peltier效应,如图 1.1(b)所示^[1]｡

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