摘 要

Bi₂Te₃基热电材料是目前发展最成熟并且已经商业化运用的一类热电材料，在热电制冷和低温热电发电方面表现出了非常大的潜力。目前商用Bi₂Te₃基热电材料都是采用区熔法批量生产，其最大热电优值ZT可达1.0，但区熔Bi₂Te₃基材料具有高度择优取向，力学性能差，导致其成品率低、不便于加工、使用过程中易破坏。所以优化材料的制备工艺以提升材料的热电优值并降低其取向性是目前研究的重点。

本论文采用熔体旋甩法(MS)结合等离子活化烧结(PAS)制备多晶n型Bi₂(Se_0.6Te_2.4)化合物，以减弱材料的择优取向，提升其热电优值。同时本论文探索了熔体旋甩和等离子活化烧结过程对n型Bi₂(Se_0.6Te_2.4)化合物取向性的影响，并探究了熔体旋甩的喷射压力参数、等离子活化烧结的烧结温度与烧结压力参数对材料的热电性能的影响，所得结果如下：

区熔样的电导率和热导率在平行于解理面方向为垂直解理面方向的4倍和2倍，研磨后进行PAS的样品取向性明显减小，两个方向热导率相差接近35%，而使用MS结合PAS工艺的样品取向性进一步减小，各性能在两个方向只相差不到5%。

固定熔体旋甩过程中铜辊转速、喷射距离、腔体压力，等离子活化烧结过程中的升温速度和烧结时间，通过改变MS喷射压力，我们发现ZT值随着喷射压力的增大先减后增，在我们选取的喷射压力范围内，0.08 MPa的样品具有最大的ZT值为0.91@475 K。

固定喷射压力为0.08 MPa，改变烧结温度，结果表明450 ℃和500 ℃烧结的样品具有接近的ZT值，分别为0.91@475 K和0.90@450 K。而烧结温度只有400 ℃的样品其性能明显较差。

固定烧结温度为450℃，我们调节烧结压力后发现，随着压力的增大，样品的取向性有略微增强，30 MPa和50 MPa的样品都具有较大的热导率，只有40 MPa的样品具有比较突出的热电优值，为0.91@475 K。

关键词：熔体旋甩；n型碲化铋基化合物；热电性能；取向性

Abstract

Bismuth telluride-based compounds, as one of the most mature and commercially used thermoelectric materials, have great potential in the field of thermoelectric(TE) cooler and low temperature power generation. Nowadays，the commercial bismuth telluride-based TE materials are manufactured by the zone melting(ZM) method and its maximum dimensionless figure of merit(i.e. ZT) reaches 1.0. However, the zone melting bismuth telluride-based materials are highly textured with large crystals and preferential orientation which results in the poor mechanical properties, low finished products ratio, inconvenience of process and damage in use. In the consequence, it’s important to improve the TE properties and decrease the degree of orientation of TE materials by the way of optimizing the preparation technologies.

In order to decrease preference orientation and improve the properties of TE materials, polycrystalline n-type Bi₂(Se_0.6Te_2.4) is synthesized by melting spinning(MS) and plasma activated sintering(PAS) in this paper. And this paper discover the effect of MS and PAS on the orientation of n-type Bi₂(Se_0.6Te_2.4) and the impact of the injection pressure in MS and the sintering pressure and temperature in PAS on the TE properties. The main contents and results are listed as follow.

The ZM samples possess 4 times higher electricity conductivity and twice higher thermal conductivity along the ab plane than c axis. But the orientation of the sample synthesized by grinding and PAS is obviously decreased and the thermal conductivity in plane is about 35 percent larger than out plane. As for the sample prepared by MS and PAS, the orientation is decreased more severely and all kinds of properties differ within 5 percent.

We fix a series of parameters, such as the roller speed, injection height and cavity pressure in MS and the rate of temperature increase and sintering time in PAS. While we change the injection pressure, we find the ZT value increase at first then decrease and the sample using a injection pressure 0.08 MPa owns the maximum ZT value of 0.91 at 475 K in the range we measured.

After that, we select the injection pressure to be 0.08 MPa and change the sintering temperature. Then we find the maximum ZT of the samples sintered at 450℃ and 500℃ are 0.91 at 475 K and 0.90 at 450 K respectively, much higher than that of the samples sintered at 450 ℃.

Similarly, we fix the sintering temperature to be 450℃ and change the pressure. We find the preferential orientation increase gradually as the pressure increase and the samples sintered at 30 MPa and 50 MPa possess larger thermal conductivities, while the sample sintered at 40 MPa show a maximum ZT of 0.91 at 475 K.

Key Words：melt spinning; n-type bismuth telluride-based compounds; thermoelectric properties; orientation

目 录

第1章 绪论…………………………………………………………………………..1

1.1 热电材料的研究背景 1

1.1.1 热电效应 1

1.1.1.1 Seebeck效应 1

1.1.1.2 Peltier效应 2

1.1.1.3 Thomson效应 3

1.1.2 热电器件及其应用 4

1.1.3 影响热电材料的物理参数 6

1.2 Bi₂Te₃基热电材料的研究现状 8

1.2.1 Bi₂Te₃基热电材料的基本性质 8

1.2.2 Bi₂Te₃基热电材料的各向异性 9

1.2.3 Bi₂Te₃基热电材料的制备技术和热电性能 10

1.2.3.1 区熔法 10

1.2.3.2 热变形法 11

1.2.3.3 熔体旋甩法 12

1.3 本论文的选题意义及主要内容 13

第2章 材料的制备及表征方法 15

2.1 实验工艺 15

2.2 材料制备方法及设备 16

2.2.1 熔体旋甩仪 16

2.2.2 等离子活化烧结 17

2.3 材料的表征与性能测试方法及设备 17

2.3.1 物相分析 18

2.3.2 微观结构分析 18

2.3.3 块体材料密度的测定 18

2.3.4 Seebeck系数和电导率的测定 18

2.3.5 热导率的测定 19

第3章 MS工艺对n型Bi₂(Se_0.6Te_2.4)热电材料微结构及热电性能的影响 21

3.1 引言 21

3.2 实验 21

3.3 MS工艺对n型Bi₂(Se_0.6Te_2.4)热电材料取向性的影响 22

3.3.1 相结构 23

3.3.2 电运输性能及功率因子 24

3.3.3 热运输性能及ZT值 25

3.4 MS喷射压力对n型Bi₂(Se_0.6Te_2.4)热电材料微结构及热电性能的影响 27

3.4.1 相结构与微观结构 27

3.4.2 电运输性能及功率因子 30

3.4.3 热运输性能及ZT值 31

3.5 本章小结 33

第4章 PAS工艺对n型Bi₂(Se_0.6Te_2.4)热电材料微结构及热电性能的影响 34

4.1 引言 34

4.2 实验 34

4.3 PAS烧结温度对n型Bi₂(Se_0.6Te_2.4)热电材料的微结构和热电性能影响.35

4.3.1 相结构与微观结构 35

4.3.2 电运输性能及功率因子 36

4.3.3 热运输性能及ZT值 37

4.4 PAS烧结压力对n型Bi₂(Se_0.6Te_2.4)热电材料的微结构和热电性能影响. 39

4.4.1 相结构与微观结构 39

4.4.2 电运输性能及功率因子 40