Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139.
Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139.
Proc Natl Acad Sci U S A. 2018 Jan 30;115(5):879-884. doi: 10.1073/pnas.1715477115. Epub 2018 Jan 16.
Recent advancements in thermoelectric materials have largely benefited from various approaches, including band engineering and defect optimization, among which the nanostructuring technique presents a promising way to improve the thermoelectric figure of merit () by means of reducing the characteristic length of the nanostructure, which relies on the belief that phonons' mean free paths (MFPs) are typically much longer than electrons'. Pushing the nanostructure sizes down to the length scale dictated by electron MFPs, however, has hitherto been overlooked as it inevitably sacrifices electrical conduction. Here we report through ab initio simulations that Dirac material can overcome this limitation. The monotonically decreasing trend of the electron MFP allows filtering of long-MFP electrons that are detrimental to the Seebeck coefficient, leading to a dramatically enhanced power factor. Using SnTe as a material platform, we uncover this MFP filtering effect as arising from its unique nonparabolic Dirac band dispersion. Room-temperature can be enhanced by nearly a factor of 3 if one designs nanostructures with grain sizes of ∼10 nm. Our work broadens the scope of the nanostructuring approach for improving the thermoelectric performance, especially for materials with topologically nontrivial electronic dynamics.
最近，热电材料的发展在很大程度上受益于各种方法，包括能带工程和缺陷优化，其中纳米结构技术通过减小纳米结构的特征长度，提供了一种提高热电优值（）的有前途的方法，这一方法基于这样一种信念，即声子的平均自由程（MFPs）通常比电子长得多。然而，将纳米结构尺寸缩小到由电子 MFPs 决定的长度尺度，迄今一直被忽视，因为这不可避免地牺牲了电导率。在这里，我们通过从头算模拟报告说，狄拉克材料可以克服这一限制。电子 MFP 的单调下降趋势允许过滤掉对 Seebeck 系数有害的长 MFP 电子，从而导致功率因子的显著增强。使用 SnTe 作为材料平台，我们发现这种 MFP 过滤效应源自其独特的非抛物狄拉克能带色散。如果设计具有约 10nm 晶粒尺寸的纳米结构，室温下的可以提高近 3 倍。我们的工作拓宽了通过纳米结构方法来提高热电性能的范围，特别是对于具有拓扑非平凡电子动力学的材料。
