Kimberly Tanner Q, Wang Evan Y C, Navarro Gustavo D, Qi Xiao, Ciesielski Kamil M, Toberer Eric S, Kauzlarich Susan M
Department of Chemistry, University of California, One Shields Avenue, Davis, California 95616, United States.
The Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, California 94720, United States.
Chem Mater. 2024 Jun 27;36(13):6618-6626. doi: 10.1021/acs.chemmater.4c01092. eCollection 2024 Jul 9.
BiTe is a well-known thermoelectric material that was first investigated in the 1960s, optimized over decades, and is now one of the highest performing room-temperature thermoelectric materials to-date. Herein, we report on the colloidal synthesis, growth mechanism, and thermoelectric properties of BiTe nanoplates with a single nanopore in the center. Analysis of the reaction products during the colloidal synthesis reveals that the reaction progresses via a two-step nucleation and epitaxial growth: first of elemental Te nanorods and then the binary BiTe nanoplate growth. The rates of epitaxial growth can be controlled during the reaction, thus allowing the formation of a single nanopore in the center of the BiTe nanoplates. The size of the nanopore can be controlled by changing the pH of the reaction solution, where larger pores with diameter of ∼50 nm are formed at higher pH and smaller pores with diameter of ∼16 nm are formed at lower pH. We propose that the formation of the single nanopore is mediated by the Kirkendall effect and thus the reaction conditions allow for the selective control over pore size. Nanoplates have well-defined hexagonal facets as seen in the scanning and transmission electron microscopy images. The single nanopores have a thin amorphous layer at the edge, revealed by transmission electron microscopy. Thermoelectric properties of the pristine and single-nanopore BiTe nanoplates were measured in the parallel and perpendicular directions. These properties reveal strong anisotropy with a significant reduction to thermal conductivity and increased electrical resistivity in the perpendicular direction due to the higher number of nanoplate and nanopore interfaces. Furthermore, BiTe nanoplates with a single nanopore exhibit ultralow lattice thermal conductivity values, reaching ∼0.21 WmK in the perpendicular direction. The lattice thermal conductivity was found to be systematically lowered with pore size, allowing for the realization of a thermoelectric figure of merit, zT of 0.75 at 425 K for the largest pore size.
BiTe是一种著名的热电材料，于20世纪60年代首次被研究，经过数十年的优化，如今是目前性能最佳的室温热电材料之一。在此，我们报告了中心带有单个纳米孔的BiTe纳米片的胶体合成、生长机制和热电性能。对胶体合成过程中反应产物的分析表明，反应通过两步成核和外延生长进行：首先是元素碲纳米棒的形成，然后是二元BiTe纳米片的生长。外延生长速率在反应过程中可以控制，从而使得在BiTe纳米片的中心形成单个纳米孔。纳米孔的尺寸可以通过改变反应溶液的pH值来控制，在较高pH值下形成直径约为50 nm的较大孔，在较低pH值下形成直径约为16 nm的较小孔。我们认为单个纳米孔的形成是由柯肯达尔效应介导的，因此反应条件允许对孔径进行选择性控制。如扫描和透射电子显微镜图像所示，纳米片具有明确的六边形晶面。透射电子显微镜显示，单个纳米孔的边缘有一层薄的非晶层。对原始的和带有单个纳米孔的BiTe纳米片的热电性能在平行和垂直方向上进行了测量。这些性能显示出很强的各向异性，由于纳米片和纳米孔界面数量较多，垂直方向的热导率显著降低，电阻率增加。此外，带有单个纳米孔的BiTe纳米片表现出超低的晶格热导率值，在垂直方向上达到约0.21 WmK。发现晶格热导率随孔径系统地降低，对于最大孔径，在425 K时实现了热电优值zT为0.75。
