Low band gap thermoelectric materials suffer from bipolar effects at high temperatures, with increased electronic thermal conductivity and reduced Seebeck coefficient, leading to reduced power factor and low ZT figure of merit. In this work we show that the presence of strong transport asymmetries between the conduction and valence bands can allow high phonon-limited electronic conductivity at finite Seebeck coefficient values, leading to largely enhanced power factors. The power factors that can be achieved can be significantly larger compared to their maximum unipolar counterparts, allowing for doubling of the ZT figure of merit. We identify this behavior in low band gap cases from the half-Heusler materials family. Using both, advanced electronic Boltzmann transport calculations for realistic material bandstructures, as well as model parabolic electronic bands, we elaborate on the parameters that determine this effect. We then develop a series of descriptors which can guide machine learning studies in identifying such classes of materials with extraordinary power factors at nearly pristine conditions. For this we test more than 3000 analytical bandstructures and their features, and more than 120 possible descriptors, to identify the most promising ones that contain: i) only band structure features for easy identification from material databases, and ii) band structure and transport parameters that provide much higher correlations, but for which parameter availability can be somewhat scarce.
Thermoelectric and Magnetic Properties in Doped Fe$_2$VAl within a Bipolar Random Anderson Model
Department of Applied Physics, Tokyo University of Science（东京理科大学应用物理系）；Research Institute for Science and Technology, Tokyo University of Science（东京理科大学科学技术研究院）
Selenium direct doping obtained high-performance-n-type Bi2Te3-based thermoelectric materials with a wide temperature range
Advanced Ceramics Research Center, School of Materials Science and Engineering, Anhui University of Technology（安徽工业大学材料科学与工程学院先进陶瓷研究中心）；Institute of Energy, Hefei Comprehensive National Science Center (Anhui Energy Laboratory)（合肥综合性国家科学中心能源研究院（安徽能源实验室））；School of Chemistry and Materials Science, University of Science and Technology of China（中国科学技术大学化学与材料科学学院）
通过高温熔炼结合退火工艺制备 n 型 Bi2Te3 基热电材料，研究硒掺杂量和退火对载流子浓度、双极效应抑制及热电性能的影响，为相关研究提供参考。
Mg$_{3+δ}$Sb$_x$Bi$_{2-x}$ family: A promising substitute for the start-of-art n-type thermoelectric materials near room temperature
半个多世纪以来，Bi 2 Te 3-xSex系列热电材料一直是近室温n型热电材料的先驱，在近室温的主动冷却和新型波收集应用中占据主导地位，但其脆性和含Te的缺点限制了其进一步的应用探索。在这里，我们表明，Mg 3 +δ SbxBi 2-x家族（（ZT）平均值=1.05）可能是一个有前途的替代Bi 2 Te 3-xSex家族（（ZT）平均值=0.9-1.0）在50-250 °C的温度范围内的热电性能相当的基础上，通过协同效应从可调带隙使用合金效应和可抑制Mg空位形成使用填隙Mn掺杂剂。前者是将最佳热电性能移到RT附近，后者有助于部分解耦电输运和热输运，以获得最佳RT功率因数。带隙的正温度依赖性表明，该家族也是一个优越的中温热电材料的显着抑制双极效应。此外，与Bi 2 Te 3-xSex家族相比，机械韧性高两倍，巩固了在RT附近的最新n型热电材料的有前途的替代品。
