能带非对称性改造提升热电性能的研究

Band engineering has been demonstrated as an effective approach for thermoelectric performance enhancement. According to the Boltzmann theory on electron transport, Seebeck coefficient is determined by the difference on the conductivity between electrons with energy above and below the Fermi level (EF). We propose a strategy for increasing the Seebeck coefficient via a local band structure engineering to increase the up-down band asymmetry near the Fermi level and therefore for increasing the conductivity difference between electrons with energy above and below EF. This work firstly intrucduces highly localized f or d electron states into PbTe by rare-earth or transition-metal elements doping, and then adjusts the positions between these localized states and the Fermi level via a careful design of dopant concentration and matrix composition. This work focuses on the evolution of the band asymmetry near EF, the mechanism on how band asymmetry affects the electronic transport properties and the development of the technology for engineering the band asymmetry in PbTe, to clarify its optimal materials design for effectively enhancing thermoelectric performance via band asymmetry engineering. Simultaneously, band asymmetry alters the dispersion relationship between electron and energy, allowing a reduction on energy exchange between transporting electrons, and therefore, reduces the electronic thermal conductivity at a given electrical conductivity. Based on the dual effects from both increase in Seebeck coefficient and reduction in electronic thermal conductivity, this work can potentially provide theoretical and experimental basis for enhancing the thermoelectric performance in PbTe or related compounds via band asymmetry engineering.

能带调控是提升热电性能的有效手段。据玻尔兹曼电子输运理论，Seebeck系数由费米能级(EF)上下电子电导率差异决定。本项目提出通过局部改造EF附近能带结构，提升其上下非对称性，增大EF上下电子电导率差异、提升Seebeck系数的研究方案。利用稀土或过渡金属元素掺杂在PbTe中引入局域化f或d电子能级，通过调节掺杂浓度及PbTe固熔体组成调整局域化电子能级与EF之间的位置匹配，研究费米能级附近能带非对称性的演变规律、及其对PbTe化合物电输运性能的作用机制，发展能带非对称性的调控技术，明确通过能带结构非对称性改造有效提升其热电性能的材料设计方案。能带非对称性改造同时调整了电子数随能量的分布，可减弱输运电子间的能量交换，在给定电导率时降低电子热导率。基于其提升Seebeck系数同时降低电子热导率的双重贡献，本研究有望为通过能带非对称性改造提升PbTe及类似化合物热电性能提供理论和实验依据。

热电能源技术将热能直接转换为电能，但转换效率较低是制约该技术大规模应用的主要瓶颈。本项目以热电材料能带调控为主要研究内容，主要围绕PbTe基及IV-VI族材料取得成果有：发展了固溶和掺杂调控能带的技术，研究能带结构对PbTe基化合物电学性能的影响，建立了能带与电输运性能的定量模型，明确了有利于提升热电性能的能带非对称性调控原则，获得了热电性能显著提升的PbTe基热电材料，为通过能带结构调控提升PbTe及类似化合物热电性能提供理论和实验依据；协同缺陷维度设计分级散射不同频率段声子，多材料体系晶格热导率降至玻璃态极限，最终获得了热电性能显著提升的PbTe基热电材料，并指导其它多材料体系热电性能获得新突破。依托本项目及同济大学的支持，申请人以通讯/第一作者身份发表期刊论文42篇，其中IF~10及高影响力的论文26篇，包括Joule(Cell姐妹刊2篇，其中1篇为封面论文)、Nat. Commu.(2篇)、Adv. (Funct., Energ.) Mat. (5篇)等。本项目实现了材料热电性能的突破，其研究成果为热电材料研究提供了指导思路与解决方案，为促进热电技术应用奠定了基础。