论文总字数：23898字

摘 要

热电材料是一种可以直接将热能转化为电能的的新型功能材料, 在废热气的二次利用、热电制冷等领域有较为广泛的应用,可以有效缓解日益严峻的能源紧缺和环境污染的问题。起初被作为光电材料的p型半导体Cu₂SnS₃由于其较窄的禁带宽度( E_g约0.9 eV)和较低的热导率而被探索应用于热电材料领域。除此之外, 它还有成本低, 毒性小, 自然储量丰富等优点, 受到了越来越多的关注。热电材料的转换效率取决于热电优值ZT, 其中决定ZT的物理量分别为赛贝克系数S、电导率σ和热导率k, 而且三者之间互相关联, 很难通过只改变一个值的大小从提升热电优值。

目前, 针对Cu₂SnS₃化合物体系的研究主要是通过Sn位受主掺杂调节载流子浓度和电导率, 进而优化功率因子和热电优值。有研究表明掺杂20%的Co的Cu₂SnS₃具有最优的热电性能, 但较高的电导率所导致的高电子热导率限制了ZT值。因此本文拟在掺杂20%的Co的基础上对Cu₂SnS₃再进行Sb替换, 最终形成目标化合物Cu₂Sn_0.8-xSb_xCo_0.2 S₃ (x = 0, 0.05, 0.10, 0.15, 0.20)。了解Sb掺杂对电输运性能和热传导性能的影响及机理, 着重考察Sb的过剩电子替换对材料的晶相组成及热电性能的影响。在假设迁移率、载流子有效质量和晶格热导率不变的条件下, 性能估算表明, 随着Sb掺杂量从x = 0增加到x = 0.2, 载流子浓度从4.35×10²¹cm^-3降低到2.61×10²¹cm^-3, 对应地高温(723 K)电导率从384 S/cm降低到263 S/cm, 塞贝克系数从156 μV/K 增大至220 μV/K, 功率因子从9.5 W/(m·K²) 显著提升至11.2W/(m·K²); 同时, 总热导率从0.80 W/( m·K)降低到0.60W/( m·K); 最终, 在掺杂量为20%, 获得最优热电优值1.3(723K), 与无Sb掺杂样品相比有显著提高。以上结果说明, Sb掺杂有望大幅提高Cu₂SnS₃体系的热电性能。

关键词: Cu₂SnS₃ 热电材料 ZT值 Sb掺杂

Effect of Sb doping on the thermoelectric properties of Cu₂Sn_0.8Co_0.2S₃

ABSTRACT

Thermoelectric (TE) material is a new type of functional material that can directly convert thermal energy into electrical energy. It is widely used in the fields of waste heat recovery and steady-state refrigeration, which helps effectively alleviate the increasingly severe energy shortage and environmental pollution. P-type Cu₂SnS₃, which was originally used as a photoelectric material, has been explored previously in the field of TE materials due to its narrow band gap (E_g about 0.9 eV) and low thermal conductivity. In addition, it has the advantages of low cost, low toxicity, and abundant natural resources, thus receiving more and more attention. The conversion efficiency of TE materials depends on the TE figure of merit ZT, which is determined by the physical parameters of Seebeck coefficient S, electrical conductivity σ, and thermal conductivity k. Because they are related to each other interdependently, it is difficult to optimize individually to improve ZT.

At present, the research on Cu₂SnS₃ is mainly to adjust the carrier concentration and electrical transport properties through Sn-site acceptor doping so as to optimize the power factor and ZT. Studies have shown that Cu₂SnS₃ doped with 20% Co has the best performance, but the high electronic thermal conductivity (k_e) due to the large σ limited the ZT value. Therefore, this paper intends to explore the potential to achieve an improved ZT by donor-doping with Sb on the basis of 20%Co-doping, by maintaining the high DOS effective mass, m, due to Co-doping while reducing k_e, and consequently the total k. In the present work, with the presumption of a maintained m, μ and lattice thermal conductivity k_lat, the transport properties were estimated theoretically. As the Sb doping amount increases from x = 0 to 0.2, the carrier concentration decreases from 4.35 × 10²¹ cm^-3 to 2.61 × 10²¹ cm^-3; Correspondingly, the σ value at 723 K decreases from 384 S/cm to 230 S/cm , while S value increases from 156 μV/K to 220 μV/K, leading to an increase of power factor S²σ from 9.5 W/(m·K²) to 11.2W/(m·K²); While the total k decreases from 0.80 W/(m·K) to 0.60 W/(m·K); Finally, the optimal ZT value of 1.3 is estimated at the doping amount of 20% at 723K, which is significantly improved compared with the sample without Sb doping. The above results indicate that Sb doping should be able to improve the TE performance of the Cu₂SnS₃ system.

Key Words: Cu₂SnS₃; Thermoelectric propeities; ZT value; Donor doping

目录

摘 要 I

ABSTRACT II

第一章 绪论 1

1.1研究背景 1

1.2 热电理论简介 3

1.2.1 赛贝克效应 3

1.2.2 帕尔贴效应 4

1.2.3 汤姆森效应 4

1.3 提高热电性能的方式 4

1.3.1提高功率因子 4

1.3.2 降低热导率的方法 5

1.4金属硫化物热电材料的研究进展 5

1.5 Cu₂SnS₃材料研究进展 6

1.5.1 CTS的晶体结构 6

1.5.2 CTS能带结构及电子传输基本性质 7

1.6 本课题的研究目的和内容 7

1.6.1 研究目的 7

1.6.2 研究内容 8

第二章 实验部分 9

2.1实验流程图 9

2.2 实验原料 9

2.3 实验仪器 9

2.4 样品制备 10

2.4.1 Cu₂Sn_0.8-xSb_xCo_0.2S₃粉体的合成 10

2.4.2 放电等离子烧结(SPS) 10

2.5 分析与表征 10

第三章 实验数据分析与讨论 12

3.1 晶体结构 12

3.1.1 未掺杂Cu₂SnS₃的晶体结构 12

3.1.2 20%Co掺杂Cu₂SnS₃ (即Cu₂Sn_0.8Co_0.2S₃) 12

3.1.3 Sb掺杂Cu₂Sn_0.8Co_0.2S₃(即Cu₂Sn_0.8-xSb_xCo_0.2S₃) 13

3.2 空穴浓度的计算 13

3.3 电导率的计算 14

3.4 赛贝克系数的计算 15

3.5 功率因子的计算 16

3.6 热导率的计算 17

3.6.1 电子热导率 17

3.6.2 晶格热导率 18

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