磁性纳米复合热电材料的磁电效应和热电性能提升研究

Relatively independent regulation of Seebeck coefficient and electrical conductivity is now a challenging problem in the field of thermoelectric materials. The research program of this project is suggested based on the convergence phenomenon of the valence band electronic structure of filled CoSb3 experimentally discovered by us. A series of magnetic nanocomposite thermelectric materials, which are composited of filled-CoSb3 matrix and nanoparticles of ferromagnetic metals, diluted magnetic semiconductor or magnetic insulator, have been prepared by nanocomposite approach. An external magnetic field is employed to adjust the magnetization direction of the nanoparticles in these magnetic nanocomposite thermelectric materials. The research works of this project are included: (1) to investigate the influences of various magnetoelectric effects produced by magnon, such as spin Seebeck effect, spin transfer torque effect, magnon-drag thermopower, and so on, on the electronic structure of filled CoSb3 under different magnetization directions; (2) to determine the properties of the magnon that can excite the electron transformation from the Co 3d5/2 fine electronic states in the conduction band maximum to the conduction band of filled CoSb3; (3) to reveal the relationship between the valence band electronic structure convergence and the electrical transport properties of filled CoSb3; (4) to clarify the physical mechanism of regulating Seebeck coefficient and electrical conductivity of filled-CoSb3 thermoelectric materials by the magnon magnetoelectric effect. The targets of this project are as followings: (1) to establish a new method for relatively independent regulation of Seebeck coefficient and electrical conductivity based on the magnon magnetoelectric effect; (2) to provide a new approach for realizing remarkable enhancement in electrical transport properties and greater breakthroughs in ZT value of filled-CoSb3 thermoelectric materials.

相对独立调控Seebeck系数和电导率是当前热电材料领域的挑战性难题。针对实验发现的填充CoSb3价带电子结构收敛现象，提出拟通过铁磁金属、稀磁半导体和磁性绝缘体纳米粒子与填充CoSb3基体的纳米复合制备磁性纳米复合热电材料，运用外加磁场调控该材料中磁性纳米粒子的磁化方向，研究不同磁化方向条件下磁振子产生的自旋Seebeck效应、自旋迁移力矩和磁振子拖曳热电势等磁电效应对填充CoSb3电子结构的影响规律，确定将填充CoSb3价带顶Co3d5/2精细电子态电子激发至导带的磁振子属性，揭示填充CoSb3价带电子结构收敛与电输运性能之间的关系，阐明磁振子磁电效应调控填充CoSb3热电材料Seebeck系数和电导率的物理机制。在此基础上，建立基于磁振子磁电效应的Seebeck系数和电导率相对独立调控方法，为实现填充CoSb3热电材料电输运性能的大幅度提高和热电性能ZT的更大突破提供新的途径。

为了获得优异的电输运性能，热电材料通常要求排除磁性杂质，这种传统认识限制了磁性纳米复合热电材料的发展。本项目以永磁非金属纳米粒子和软磁金属纳米粒子作为第二相掺杂相、以(Ba,In)双原子填充方钴矿作为基体热电材料，开展了磁性纳米复合热电材料的组成设计、制备方法和电热输运物理机制的系统研究，同时研究了填充方钴矿热电材料精细结构与热电性能提升之间的依存关系和多种局域输运行为的共存机制及其对电输运和热输运的协同调控作用。取得了以下主要成果：.设计并制备了一系列由BaFe12O19永磁纳米粒子（BaM-NPs）和Ba0.3In0.3Co4Sb12基体热电材料组成的磁性纳米复合热电材料。发现BaM-NPs由铁磁向顺磁转变的磁性相变可以控制磁性纳米复合热电材料的电输运行为；BaM-NPs表现出可使复合材料获得高ZT值的“电子库”作用，居里温度以下起俘获电子作用，在居里温度以上释放俘获电子；BaM-NPs在复合材料中除增强声子散射外，还产生了电子螺旋运动和磁振子拖拽热电势两种磁电效应。在此基础上，建立了利用永磁非金属纳米粒子铁磁/顺磁转变产生的磁电效应抑制热电材料本征激发下热电性能劣化的新方法，并利用该新方法研制出了In填充方钴矿基磁性纳米复合热电材料。.设计并制备了一系列由软磁金属Co纳米粒子和Ba0.3In0.3Co4Sb12基体热电材料组成的磁性纳米复合热电材料Co/Ba0.3In0.3Co4Sb12。发现嵌入在基体热电材料中的软磁金属纳米粒子在经历由铁磁向超顺磁转变的磁性相变过程中产生了三种热电磁效应，它们分别是由软磁金属纳米粒子向基体热电材料的电荷转移、由超顺磁性产生的电子多重散射和由单磁畴随机转动以及纳米结构产生的增强声子散射，这些热电磁效应能够在纳米和介观尺度上有效调控纳米复合热电材料中电子/声子输运和大幅度提高热电性能。.发现在In填充方钴矿热电材料中同时存在可以实现电热输运协同调控的电子加速运动、费米能级附近态密度增大和声子共振散射等三种局域输运行为共存；(Ba,In)双原子方钴矿的热电性能提升起源于能带收敛、费米能级附近的态密度增加和(Ba,In)填充原子共振声子散射。