热电功能基元多层次序构超高性能室温热电材料及新输运机制研究

High performance room temperature thermoelectric materials could be used for all solid highly-efficient heat dissipation and for thermoelectric power generation, thus, are promising for important applications. Due to limitations of the strong coupling among each thermoelectric transport parameters and their low overall performances, it is difficult to achieve excellent ZT values in thermoelectric materials. In order to make significant breakthroughs over the performances of present room temperature thermoelectric materials, we propose a new optimization strategy via creating new thermoelectric materials by a multi-level sequential assembly process utilizing molecular beam epitaxial growth technique. Thermoelectric functional units with multi-valley band structure and with band possessing a linear energy-momentum relation are designed and are then sequentially assembled for preparing new thermoelectric compounds in the scale of atomic and lattice size. The goal is to investigate new effects for realizing strong coupling of electronic states from two functional units as well as for creating new crystal structure with low thermal conductivity originated from two functional units and their sequential assembly, and to reveal new regulation mechanisms for simultaneously obtaining high electrical conductivity, high Seebeck coefficient and low thermal conductivity. In addition, the sequential assembly of the created new thermoelectric compounds in the size of nanometers will result in new structured thermoelectric materials. The motivation is to investigate multiple new effects related to size and interface introduced by functional units and their sequential assembly, such as the quantum confinement effect, the interfacial phonon scattering effect and so on, and to clarify new transport mechanisms for decoupling and remarkably enhancing each thermoelectric transport parameters though the concurrent application of multiple transport effects. Through optimizing intrinsic thermoelectric properties in the lattice-size level and by further enhancing each thermoelectric transport parameters in the micron-size level, the fabricated assembled new materials could hopefully achieve ultra-high room temperature thermoelectric performances, with ZT exceeding 2.0.

高性能室温热电材料可用于全固态高效散热和热电发电，具有重要的应用前景。由于各热电输运参数的总体性能不高以及存在强耦合关联，热电材料难以获得高ZT值。为大幅突破现有室温热电材料的性能水平，本项目提出分子束外延技术多层次序构热电新材料的优化新思路。通过设计具多电子能谷以及线性色散电子态的功能基元并在原子、晶格层次有序构造热电新化合物，研究两种基元的电子态实现耦合统一以及两种基元序构低热导晶体结构的新效应，阐明同时获得高Seebeck、高电导和低热导的调控新机制。在此基础上，由不同热电新化合物在纳米微观层次有序构造新结构热电材料，研究功能基元结合序构引入的量子限域效应、界面声子散射效应等多种尺寸和界面新效应，阐明多种新效应叠加应用解耦和独立优化各输运参数的新机制。通过在晶格层次显著优化本征热电性能以及在微观层次进一步优化各热电输运参数，创制的序构新材料有望获得超高室温热电性能，其ZT突破2.0。

功能基元序构高性能热电新材料及电热输运解耦和大幅优化是热电领域高度关注的研究课题。本项目以Bi2Te3、Sb2Te3、Mg3Sb2、Mg3Bi2、SnTe、MnTe等热电化合物和拓扑材料作为功能基元，通过界面特性和薄膜工艺参数设计和匹配，可控制备出Bi2Te3/1T’-MoTe2、Sb2Te3/MnTe以及Mg3Sb2/Mg3Bi2等新型异质结和超晶格薄膜，发现功函数差异引起界面电荷作用，及其产生的电荷注入、能量过滤效应、调制掺杂等新效应，实现热电输运参数的全面优化，制备出具有高热电性能的热电薄膜新材料，并开发出具有特殊电子结构特征的Bi2Te3/1T’-MoTe2新型异质结薄膜。取得的重要成果概述如下。.（1）发现MBE薄膜工艺参数和缺陷结构调控是大幅度优化Bi2Te3、Mg3Sb2、SnTe、MnTe等功能基元的载流子输运和电输运性能的重要途径。以TeBi反位缺陷为主要缺陷的n型Bi2Te3薄膜获得最高功率因子达5.05 mWm-1K-2。.（2）在1T’-MoTe2/Bi2Te3、Sb2Te3/MnTe和Mg3Sb2/Mg3Bi2等功能基元序构超晶格薄膜中发现功函数差异引起电荷注入、能量过滤效应、调制掺杂等电热输运优化新效应，实现了各热电输运参数的同步优化。.（3）成功制备出1T’-MoTe2/Bi2Te3范德华异质结薄膜，发现功函数差异引起了强界面作用和SOC临近效应，引起半金属特征单层1T’-MoTe2向有带隙量子自旋Hall绝缘态转变的新现象，为通过异质界面效应调控电子结构和热电性能提供了一条新的思路。.本项目实施期间已发表SCI论文8篇，培养博士生3名，硕士生1名。圆满完成了功能基元序构热电新材料及阐明电热输运新效应的研究任务，所取得的成果对进一步利用功能基元结合序构大幅度提升热电性能提供了重要指导和借鉴。