硬/软磁纳米粒子共存的磁性热电材料交换耦合作用和热电磁效应研究

The simultaneous realization of synergetic manipulation of electron/phonon transport at nanometre and mesoscopic length scales and the suppression of the performance deterioration under the intrinsic excitation region is now a challenging problem in the field of thermoelectric materials. The research program of this project is suggested based on the exchange coupling interaction and thermoelectromagnetic effect induced by magnetic phase transition of mixed magnetic nanoparticles experimentally discovered by us. A series of mixed magnetic nanocomposite thermelectric materials, which are composited of filled skutterudite matrix and mixed magnetic nanoparticles including hard and soft magnetic nanoparticles, have been prepared by nanocomposite approach. The research works of this project are included: (1) to investigate the influences of exchange coupling interaction and thermoelectromagnetic effect induced by magnetic phase transition of mixed magnetic nanoparticles on magnetic properties, electronic structure and thermoelectric transport properties of filled skutterudite; (2) to reveal the relationship between the exchange coupling interaction, thermoelectromagnetic effect and magnetic properties, thermoelectric transport properties of filled skutterudite; (3) to clarify the physical mechanism of regulating electron/phonon transport and suppressing the performance deterioration under the intrinsic excitation region of filled skutterudite by the exchange coupling interaction and thermoelectromagnetic effect induced by mixed magnetic nanoparticles. The targets of this project are as followings: (1) to establish a new method for simultaneously regulating the electron/phonon transport at nanometre and mesoscopic length scales and suppressing the performance deterioration under the intrinsic excitation region of filled skutterudite by the exchange coupling interaction and thermoelectromagnetic effect; (2) to provide a new approach for realizing remarkable enhancement in thermoelectric properties and greater breakthroughs in ZT value of filled skutterudite thermoelectric materials.

同时实现在纳米-介观尺度电子/声子输运的协同调控和本征激发下性能劣化的抑制是当前热电材料领域的挑战性难题。针对硬/软磁混合纳米粒子之间存在交换耦合作用及磁性相变产生热电磁效应的现象，提出通过将硬磁纳米粒子和软磁纳米粒子组成的混合磁性纳米粒子与填充方钴矿基体复合制备硬/软磁纳米粒子共存的磁性纳米复合热电材料。研究磁性纳米复合热电材料中两种磁性纳米粒子的交换耦合作用和磁性相变引起的热电磁效应对填充方钴矿磁性能、电子结构和电热输运性能的影响规律。揭示交换耦合作用和热电磁效应与磁性能和电热输运性能之间的关系，阐明交换耦合作用和热电磁效应协同调控填充方钴矿材料电子/声子输运并抑制本征激发下性能劣化的物理机制。在此基础上，建立基于交换耦合作用和热电磁效应协同调控填充方钴矿电子/声子输运并抑制本征激发下性能劣化的调控方法，为实现填充方钴矿材料热电性能的更大突破提供新的途径。

同时实现在纳米-介观尺度电子/声子输运的协同调控和本征激发下性能劣化的抑制是当前热电材料领域的挑战性难题。本项目以解决该挑战性难题为目标，首先优化n型或p型填充方钴矿基体的热电性能，然后将硬、软或硬/软磁纳米粒子与填充方钴矿基体复合制备磁性纳米复合热电材料，对磁性纳米粒子的磁性相变引诱的热电磁效应对填充方钴矿结构、磁性能和电热输运性能的影响规律进行了系统研究。取得了以下主要研究成果：. (1)发展了一种制备高性能具有涡旋-条状晶粒结构的n型填充方钴矿基体材料的方法。对采用熔融旋甩结合放电等离子体烧结（SPS）工艺制备的n型方钴矿材料微结构和相变机理进行系统研究并给出了热力学解释。在n型In0.25Co4Sb12和Ba0.3In0.3Co4Sb12填充方钴矿基体材料中引入硬磁性（BaFe12O19）或硬/软磁（BaFe12O19+Co）纳米粒子，硬磁纳米粒子的“电子库效应”可以有效抑制基体高温本征激发导致的性能恶化；软磁纳米粒子的超顺磁性产生的热电磁效应可以协同优化基体的电热输运性能；同时，硬/软磁混合纳米粒子之间的交换耦合作用和磁性相变产生的热电磁效应可以有效抑制基体本征激发下性能劣化并在纳米-介观尺度协同调控电子/声子输运。其中，0.35%(BaFe12O19+4Co)/Ba0.3In0.3Co4Sb12混合磁性热电材料在650-850 K的宽温区获得一个最大平均热电优值ZT为1.7。. (2)通过优化烧结温度和合金化工程提升了Ce填充方钴矿材料的热电性能。在p型CeFe3.8Co0.2Sb12填充方钴矿基体材料中引入硬磁性BaFe12O19纳米粒子，硬磁纳米粒子的“电子库效应”可以有效抑制p型方钴矿基体高温本征激发导致的性能恶化。其中，p型方钴矿基磁性热电材料0.15%BaFe12O19/CeFe3.5Ni0.3Co0.2Sb12在800 K时取得最高的ZT值约0.8。. 基于以上研究成果，本项目基本建立了基于交换耦合作用和热电磁效应协同调控填充方钴矿电子/声子输运并抑制本征激发下性能劣化的调控方法，并为实现填充方钴矿材料热电性能的更大突破提供了新的途径。