Ca2Si基半导体的空穴浓度及晶格热导率协同调控优化热电性能研究

Orthorhombic Ca2Si-based semiconductor materials will be fabricated by using tantalum tube weld melting and vacuum hot pressing methods. Microstructure of Ca2Si and doped Ca2Si can be characterized by XRD, EDS and HRTEM. Effects of Li and Ag co-doping on the hole concentration of Ca2Si are investigated. In this way, the optimum hole concentration range of Li and Ag co-doped Ca2Si can be confirmed. The optimum thermoelectric power factor can be obtained. On the base of Li and Ag co-doped Ca2Si, effects of Ba-doped Ca(2-x-y)LixAgySi and Sn-doped Ca(2-x-y)LixAgySi on the lattice thermal conductivity and thermoelectric properties will be investigated. Thermoelectric properties of Ca2Si will be improved by tuning the hole concentration and the lattice thermal conductivity.The effects of doping on microstructure and band gap width will be explained. The effects of doping concentration on the form and distribution of in situ precipitation of secondary phase will be revealed, and the relationship will be investigated between the changes of the microstructure and thermoelectric properties.Tuning the hole concentration and the lattice thermal conductivity of Ca2Si-based semiconductors for improving thermoelectric properties will be studied in this project, which is a very meaningful exploration and innovation at home and abroad. The theory and system of environment friendly semiconductor thermoelectric materials can be enriched and developed. And thermoelectric properties of Ca2Si will be improved via the project. The studies are involved in important academic value and broad application prospect.

采用钽管封装熔炼及真空热压法制备正交相Ca2Si基半导体材料，利用XRD、EDS和HRTEM等技术表征材料的显微结构。 研究Li和Ag共掺杂对Ca2Si空穴浓度的影响，确定Li和Ag共掺杂Ca2Si的最佳载流子浓度范围，并获得最佳的热电功率因子。 在Li和Ag共掺杂Ca2Si的基础上，分别研究Ba掺杂、Sn掺杂对Ca(2-x-y)LixAgySi晶格热导率及热电性能的影响，通过空穴浓度及晶格热导率的协同调控优化Ca2Si的热电性能。并阐明掺杂对材料的微结构和禁带宽度的影响，揭示掺杂浓度对化合物中原位析出第二相的形式和分布情况，以及微结构的变化对热电性能的影响规律。本项目开展Ca2Si基半导体的空穴浓度及晶格热导率协同调控优化热电性能，这在国内外是一项很有意义的探索和创新，对于丰富和发展环境友好型半导体热电材料的理论和体系，进一步提高Ca2Si的热电性能都具有重要的学术价值和广阔的应用前景。

Ca2Si作为环境友好型热电材料之一，在高温发电领域有重要的应用前景。本项目采用钽管封装熔炼结合热压烧结技术制备了Ca2Si基块体热电材料。在300-873K温度范围内分别研究了Ag、Ba、Li部分替代Ca掺杂，Sn部分替代Si掺杂对Ca2Si热电性能的影响。此外，还研究了Ag和Sn双掺杂对Ca2Si热电性能的影响。Ca(2-x)AgxSi (x=0.02)样品与Ca2Si 样品相比较，热电无量纲优值ZT在300–873K 温度范围得到了优化。在550-873K温度范围内，BaxCa(2-x)Si (x=0.01)表现了较高的热电优值ZT，873K时的最大ZT值为0.17。随着Li掺杂浓度的增加，电导率逐渐增大，泽贝克系数则逐渐减小。在300-873K温度范围内，LixCa(2-x)Si (x=0.04，0.06，0.08)样品的功率因子均下降。 在650K到873K的温度范围内， Li掺杂浓度为x=0.02的功率因子得到了提高。Li掺杂浓度为x=0.02时，在650K到873K的温度范围内， Li掺杂优化了Ca2Si的热电优值，在873K的最大热电无量纲优值为0.20。随着Sn掺杂浓度的增加，电导率逐渐增大，Seebeck系数则减小。在300-873 K温度范围内，Ca2Si(1-x)Snx (x=0.02)的热导率得到明显地改善，其热导率都低于Ca2Si的热导率。在550-873K温度范围内，Ca2Si(1-x)Snx (x=0.02)表现了较高的ZT值，873K时的最大ZT值为0.22。通过在Ca位固溶Ag和Si位固溶Sn相结合， Ag和Sn双掺杂大幅度提高了电导率，在550K到873K的温度范围内，Ag和Sn双掺杂的热电功率因子与Ca2Si的相比较得到了较大地提高。Ag和Sn双掺杂的热导率也得到了优化，在300-873K温度范围内，Ca1.98Ag0.02Si(2-x)Snx(x=0.02, x=0.04)的热导率与Ca2Si的热导率相比较均有所减少。在550K到873K的温度范围内，双掺杂样品的热电功率因子及热导率都得到了优化，从而优化了Ca2Si半导体材料高温区域的热电无量纲优值ZT，Ca1.98Ag0.02Si(2-x)Snx(x=0.02)在873K时的最大ZT值达到0.27。

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