从笼形团簇的组装出发设计新型高热电优值材料

Thermoelectric materials are promising in solving the energy crisis and environmental problem due to their special ability to directly convert waste heat into electric power. For experimental research, however, it is a challenging subject to increase the thermoelectric conversion efficiency of materials because of the mutual coupling of multi physical parameters in the thermoelectric figure of merit. Based on the idea of "material genomics", it will be an important method to search new thermoelectric materials by using high-throughput calculation which can largely save the experimental cost and shorten the experimental period. Herein, on the basis of the physical fact " The lattice thermal conductivity of Clathrate can be significantly reduced through the vibration of encapsulated atom " and our previous studies of cluster-assembled materials, we propose to perform first-principles high-throughput assembly design of cage-like clusters with a wider range of composition and size in order to search the stable semiconductor materials which possess both light-band and heavy-band in their electronic structure. For these selected materials, we then investigate their thermoelectric transport properties by using the semiclassical Boltzmann theory and rigid band approximation. We will also try different methods, such as encapsulated doping of different atom, changing pattern of inter-cluster polymerization, or applying external pressure, to enhance their thermoelectric figure of merit. Meanwhile, we will explore the regulation mechanism of thermoelectric properties from the microstructural perspective. Eventually, we will be able to predict some new energy materials with high thermoelectric conversion efficiency, which can provide useful information for the further experimental research.

热电材料由于具有将废热直接转换成电能的特性，因此在解决能源危机和环境问题方面存在着诱人的应用前景。然而，热电优值多物理参数的互动耦合，使得材料热电转化效率的提高成为一个极具挑战性的实验课题。基于“材料基因组学”思想，借助高通量的计算搜索来发展新型热电材料是节约实验成本、缩短实验周期的重要手段。申请人立足“笼合物可通过内嵌原子的腔内振动大幅降低晶格热导率”的物理事实，结合在团簇组装方面的工作基础，提出对较宽化学成分和尺寸范围的笼形团簇开展第一性原理高通量组装设计，计算筛选出稳定的、能带中既有轻带又有重带的半导体材料。在此基础上，采用半经典玻尔兹曼理论和刚带近似方法计算组装材料的热电输运性能；尝试通过不同原子的内嵌掺杂、团簇间聚合方式的改变、外压作用等来提高组装材料的热电优值，并从微结构上探究其调控机理，最终预测出具有高热电转换效率的新型能源材料，为实验研究提供理论参考。

本项目以设计和预测新型高效热电材料（高电导、低热导）为目标，围绕项目研究内容和年度计划，并结合课题相关的最新国内外研究动态与实际科研条件，较好完成了项目任务，达到了考核标准。主要研究内容、重要结果及关键数据概括如下：.1. 以实验合成的II-VI族半导体笼状团簇为基元，通过组装设计，成功预测了4种新型CdO团簇组装低密度多孔材料。在优化几何结构的基础上，系统计算了4种晶相的声子谱、电子结构及电导特性。结果表明，稳定的SOD-CdO结构，不仅拥有较已有结构更好的稳定性，而且具有比传统材料更优异的电导特性，其电子迁移率达9.6×10^3 cm^2V^-1s^-1。相关成果以封面文章发表J. Phys. Chem. C上。.2. 为研究内嵌原子对团簇组装材料热导的影响和调控，项目在实施过程中采用卤素原子内嵌II-VI/III-V族半导体笼形团簇方式来设计组装基元。计算表明，核壳模式有利于基元团簇提高电子亲和能（5.36 eV），形成超卤素团簇。这为低热导材料的设计提供了基元基础。相关成果发表在Nanoscale上。.3. 结合最新科研进展，立足Dirac 拓扑材料拥有高电导率的物理事实，项目组将课题的部分研究内容拓展至Dirac材料的设计上，并预测出了多种新奇的量子态及相应的高电导量子材料，如硅基节线Dirac半金属，自旋谷耦合Dirac半金属，单自旋Dirac half metal YN2 （费米速度达3.74×10^5 m/s）。相关成果分别发表在J. Phys. Chem. Lett.，Mater. Horiz.和Nano Res.上。 .以上研究结果不仅从团簇组装的角度，为新型热电材料的开发提供了新思路，而且为基于Dirac拓扑材料设计新型热电材料奠定了理论基础。