Programme

I.8 -- Invited, VCTP-51

Date: Tuesday, 4 August 2026

Time: 16:00 - 16:40

First-Principles Study of Thermoelectric Materials Design: High-Entropy and Goniopolar Systems

Hidetomo Usui

Department of Engineering Science, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan

Thermoelectric materials design requires an understanding of the relationship between crystal structure, electronic structure, and transport properties. In this study, we present first-principles evaluations of thermoelectric materials based on two different design concepts: high-entropy alloying and goniopolarity. High-entropy alloying is based on chemical disorder in multicomponent systems, whereas goniopolarity is characterized by crystallographic-direction-dependent carrier polarity for anisotropic thermoelectric responses. High-entropy alloying has been shown to reduce lattice thermal conductivity and enhance thermoelectric performance in PbSe-based chalcogenides [1], while other high-entropy chalcogenides exhibit only moderate performance despite their ultra-low lattice thermal conductivity [2]. Motivated by these studies, we investigate PbSe-based high-entropy thermoelectric materials using the KKR-CPA method to clarify how elemental substitution affects the electronic states and thermoelectric properties. For the goniopolar case, we focus on layered Zintl-phase Mg$_3$Sb$_2$ and Mg$_3$Bi$_2$, which exhibit axis-dependent conduction polarity [3]. First-principles calculations show that this behavior originates from band anisotropy near the Fermi level: electron bands mainly contribute to in-plane conduction, while hole bands dominate cross-plane conduction. This direction-dependent carrier polarity provides a possible route to transverse thermoelectric conversion. By comparing these two cases, we discuss how elemental substitution and band anisotropy affect thermoelectric transport properties. Our results provide insight into thermoelectric materials design based on electronic-structure control. References: [1] B. Jiang et al., Science 371, 830 (2021). [2] A. Yamashita et al., Materials Research Letters 9, 366 (2021). [3] Y. Goto et al., Chemistry of Materials 36, 2018 (2024).

Presenter: Usui Hidetomo