硒化亚铜基纳米复合材料的热电物性调控研究与高效制备

Superionic Cu2Se is one of the most promising mid- and high-temperature thermoelectric materials, while copper will precipitate at one end of the tested sample under concurrent high temperature and intense electric current, and evaporation of selenium also occurs at high temperatures, both the electro-thermal stability and thermoelectric figure-of-merit needed to be further enhanced. In this project, we aim to improve the electro-thermal stability and thermoelectric figure-of-merit by the effective confinements of copper migration and selenium evaporation in the porous bulks of (1-x)Cu2Se/(x)CuXSe2 (X=Al, Ga, In) nanocomposites. On the one hand, for the cubic Cu2Se and tetragonal CuXSe2, the slight lattice mismatch (<5%) within the ab plane as well as the similar packing for selenium atoms ensure the coherency at the Cu2Se/CuXSe2 interfaces, which could restrain the copper migration and selenium evaporation as well as improve the electro-thermal stability. On the other hand, the scattering of phonons with different frequencies could be greatly enhanced because of the increased defect types and amounts in polycrystalline nanocomposite bulks, which finally lead to decreased thermal conductivity and increased thermoelectric figure-of-merit. High stability and thermoelectric figure-of-merit will be simultaneously expected for the (1-x)Cu2Se/(x)CuXSe2 nanocomposites by the synergistic effects of the nano-sized microstructure, trace second phase and porous structure in optimizing the thermoelectric performance of copper selenium based thermoelectric materials. In this project, the porous polycrystalline bulks will be fabricated by the high energy ball milling followed by the spark plasma sintering. The success implement of this project not only paves the way for the utilization of copper selenium based materials in the thermoelectric area, but also provides new ideas for the thermoelectric performance enhancement of other thermoelectric materials.

硒化亚铜快离子导体类热电材料在中高温区呈现良好应用前景，但其在高温强电流下会析出铜且硒易挥发，其稳定性与热电优值均有待提高。本项目拟通过制备多孔(1-x)Cu2Se/(x)CuXSe2(X=Al,Ga,In)纳米复合材料多晶块体，抑制Cu+迁移与硒挥发，提高其稳定性与热电优值。一方面，立方Cu2Se与四方CuXSe2在ab平面内点阵失配率<5%，易在两相界面处形成共格界面，进而抑制Cu+迁移与硒挥发，改善材料稳定性；另一方面，纳米多晶样品内缺陷种类及数量均增多，各频率声子散射增强，热导率降低，热电优值得到提高。本研究充分发挥纳米微观结构、第二相与多孔结构优化材料热电性能的协同作用，采用高能球磨与放电等离子体烧结技术高效制备具有高稳定性与高热电优值的(1-x)Cu2Se/(x)CuXSe2多晶块体。本项目的顺利实施不仅可推动该类材料在热电领域的应用，也为其它热电材料热电性能的优化提供借鉴。

项目背景.热电转换技术能实现热能和电能间的直接转化，具有高稳定性、无噪音、无污染、无需维护与环境友好等优点，可用于制冷与回收废热发电领域，受到科研工作者的广泛关注。在众多热电材料中，Cu2-xSe快离子导体类热电材料在未进行元素掺杂或微观结构纳米化的情况下已具有较高热电优值，同时其组成元素毒性小、地壳中含量高，在中高温区呈现非常好的应用前景。尽管科研工作者们已进行了深入研究，该类热电材料的热电性能也有了一定程度的提升，但其仍面临一些亟待解决的难题。基于此背景，本项目提出了通过制备(1-x)Cu2Se/(x)CuXSe2纳米复合材料，调控样品化学组成、微观结构及制备工艺，抑制多晶样品内的Cu+迁移与硒挥发，提高其电热稳定性与热电优值。.主要研究内容.对(1-x)Cu2Se/(x)CuXSe2体系电荷密度、电子能带结构与态密度、声子色散谱与态密度、格林内森常数与电热输运性质相关参数进行理论计算，研究材料化学组成对其电热输运性质的影响；利用高能球磨与放电等离子体烧结技术高效制备多孔纳米多晶样品；对多晶样品的微观结构与电热输运性质进行表征与调控。.重要结果与关键数据.通过构建Cu2Se/CuXSe2异质结并对其电热输运相关性质进行理论计算，结果表明，与单一相Cu2Se相比，异质结构费米能级处的态密度有所提高。因此，可以预测掺入微量CuXSe2后，多晶样品的电输运性质将会优化。.经过反复查阅文献和摸索高能球磨与放电等离子体烧结工艺参数，成功制备具有不同晶粒尺寸的Cu2Se/CuXSe2多晶块状样品。Cu2Se/CuXSe2多晶样品内的声子散射因其纳米微观结构与异质结界面的存在得到增强，热导率相比纯Cu2Se有显著降低，多晶样品的热电优值得到了提高。同时，由于多晶样品界面处Cu、Se与X间强的电荷相互作用，高温下样品内的Cu+迁移与硒挥发得到抑制，材料电热稳定性也得到了提升。.科学意义.本项目的顺利实施对实现硒化亚铜快离子导体类热电材料在热电转换器件中的成功应用具有重要意义，同时也为其它热电材料热电优值的提高提供了一种思路，具有重要的理论意义和工程应用价值。