State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, 150001 Harbin, China.
Department of Physics, University of Houston, Houston, TX 77204-5005.
Proc Natl Acad Sci U S A. 2018 May 22;115(21):5332-5337. doi: 10.1073/pnas.1802020115. Epub 2018 May 7.
Germanium telluride (GeTe)-based materials, which display intriguing functionalities, have been intensively studied from both fundamental and technological perspectives. As a thermoelectric material, though, the phase transition in GeTe from a rhombohedral structure to a cubic structure at ∼700 K is a major obstacle impeding applications for energy harvesting. In this work, we discovered that the phase-transition temperature can be suppressed to below 300 K by a simple Bi and Mn codoping, resulting in the high performance of cubic GeTe from 300 to 773 K. Bi doping on the Ge site was found to reduce the hole concentration and thus to enhance the thermoelectric properties. Mn alloying on the Ge site simultaneously increased the hole effective mass and the Seebeck coefficient through modification of the valence bands. With the Bi and Mn codoping, the lattice thermal conductivity was also largely reduced due to the strong point-defect scattering for phonons, resulting in a peak thermoelectric figure of merit () of ∼1.5 at 773 K and an average of ∼1.1 from 300 to 773 K in cubic GeMnBiTe. Our results open the door for further studies of this exciting material for thermoelectric and other applications.
碲化锗（GeTe）基材料具有有趣的功能，从基础和技术角度来看都得到了广泛的研究。然而，作为一种热电材料，GeTe 在约 700 K 时从菱方结构向立方结构的相变是阻碍其在能量收集方面应用的主要障碍。在这项工作中，我们发现通过简单的 Bi 和 Mn 共掺杂可以将相变温度抑制到 300 K 以下，从而在 300 到 773 K 范围内实现了立方 GeTe 的高性能。我们发现 Ge 位的 Bi 掺杂会降低空穴浓度，从而提高热电性能。Ge 位的 Mn 合金化通过改变价带同时增加了空穴有效质量和 Seebeck 系数。通过 Bi 和 Mn 共掺杂，晶格热导率也由于声子的强点缺陷散射而大大降低，导致立方 GeMnBiTe 在 773 K 时的峰值热电优值（ZT）约为 1.5，在 300 到 773 K 范围内的平均 ZT 约为 1.1。我们的结果为进一步研究这种用于热电和其他应用的令人兴奋的材料开辟了道路。
