基于ALD技术的热电材料晶粒尺寸-界面协同优化及热电输运特性

Thermoelectric materials allowing direct conversion of heat into electricity have drawn worldwide interests for decades due to their potential application in energy harvesting from wasted heat sources. Tuning the electron and phonon transport properties to partially decouple electrical conductivity and Seebeck coefficient and thermal conductivity is a basic principle on the development of high performance thermoelectric material. The grain boundary engineering in thermoelectric materials has been considered as an effective way to solve the above problems, since it can enhance Seebeck coefficient without hurting electrical conductivity much, resulting in a net enhancement in S2σ. Unfortunately, the effects of interfacial structure, composition, and morphology on these mechanisms are not yet fully clear at a quantitative level because it is difficult to control both the chemical composition and the dimension of boundaries by the traditional approach. Taking into account the advantages of ALD, we herein propose an ALD-based general bottom-up strategy to design and control grain boundary and investigate the relationship between grain boundary and the electron/phonon transportation behavior. The motivation of this work is to explore the relationship between grain boundary and the electron/phonon transportation behavior, which will finally contribute to the development of high performance TE materials. The further prospect of this study is to modify the interface potential barrier by depositing other semiconductor layer (such as SnO2, TiO2) on the matrix and further extending the ALD based atomic scale grain boundary modification strategy to other thermoelectric materials system. This study creates an initial attempt to modify the grain boundary of bulk thermoelectric materials in atomic scale by ALD process, which provides the insights for the structural design and synthesis of broadly functional hybrid thermoelectric material system.

热电材料可以实现将热能和电能的直接转换，在低品位废热利用方面具有巨大的应用前景，是目前研究的热点之一。调控热电材料中热电输运特性，实现决定热电性能基本参数的去耦合化调节，是热电材料研究的核心问题。晶粒界面工程可以有效的实现上述目的，可以在不损害电导率的前提下有效增大塞贝克系数，从而提高功率因子；同时通过增强界面声子散射降低热导率。但是，目前缺乏有效的技术手段实现对界面化学成份及结构的精确控制，晶粒界面对热电传输的作用机制尚不明确。本项目提出基于原子层沉积技术（ALD）对热电材料晶粒尺寸-界面协同调控的思想，实现热电输运的去耦合化调控，提高材料的热电性能。通过多次球磨-ALD制备技术，系统的调控材料的晶粒尺寸及界面特性，建立界面化学组分、微观结构、晶粒尺寸、及热电输运行为的对应关系。这种基于ALD原子尺度的界面修饰方法可以推广到其他的热电材料体系，为发展高性能基室温热电材料提供有益的探索。

热电材料可以实现将热能和电能的直接转换，在低品位废热利用方面具有巨大的应用前景，是目前研究的热点之一。调控热电材料中热电输运特性，实现决定热电性能基本参数的去耦合化调节，是热电材料研究的核心问题。但是，目前缺乏有效的技术手段实现对界面化学成份及结构的精确控制，晶粒界面对热电传输的作用机制尚不明确。本项目基于原子层沉积技术（ALD）对热电材料晶粒尺寸-界面协同调控的思想，实现热电输运的去耦合化调控，提高材料的热电性能。该项目研究表明（1）通过针对界面层的结构、化学组份的精确设计，商用n型Bi2Te2.7Se0.3热电材料，其最大的ZT值从0.72提高到1.01，增加了40%。（2）通过过液相辅助的晶粒界面调控的方法，可以协同调节界面微结构及晶粒尺寸，达到优化材料的热电性能的目的，其最大的ZT值达到1.21，远高于最初商用材料的性能。（3）本项目提出基于原子层沉积技术（ALD）对热电材料晶粒尺寸-界面协同调控的思想，是一种普适的热电材料性能调控手段，可以进一步推广到如半哈斯勒合金、p-型BST等其他热电材料体系。总体而言，该项目通过对晶界成分及结构的原子尺度调控，初步阐明了热电材料晶粒尺寸-界面的协同作用机制，为发展高性能室温热电材料提供理论依据和实验参考。

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