Thermoelectric calculation at finite temperature: towards environmentally benign thermoelectric materials

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K14922
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Energy engineering
• Research Institution: The University of Tokyo (2019); Osaka University (2017-2018)
• Principal Investigator: Hirayama Naomi 東京大学, 物性研究所, 特任研究員 (70581750)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 第一原理計算 / 熱電材料 / シリサイド / 不純物効果 / 熱電輸送現象

Outline of Final Research Achievements

First, we theoretically investigated Mg2Si with various p-type dopants and found that they exhibit comparable formation energies for different impurity sites, which may explain the experimental instability of their p-type conductivity. Furthermore, our calculation predicted new acceptors (Cl and F). We also revealed that the enhancement of power factor by increasing the lattice constant originates from a larger effective mass of bottom conduction bands.
Next, we investigated the fluorine doping in LaOBiS2-type layered compounds and found that the structural phase is closely related to the doping―monoclinic distortion of the mother compound decreases the capability of Fluorine doping.
Finally, our analysis of semiconducting carbon nanotubes showed that their thermoelectric performance depends on the distribution of vacancies, which suggests the possibility of thermoelectric performance improvement by controlling the structural properties including defects.

Free Research Field

物性理論

Academic Significance and Societal Importance of the Research Achievements

近年，エネルギー資源の枯渇と環境汚染の問題が加速するなか，熱エネルギーを電気エネルギーに直接変換する熱電変換技術の本格的な普及が望まれる．しかし，既存の主要な熱電材料の多くは，毒性や資源希少性の問題があり，実用化には限界があった．本研究では，環境低負荷型熱電材料の性能向上にむけて，第一原理計算に基づく材料設計指針の提案を行った．キャリア密度制御のため，安定な不純物ドーピングを実現する方法を検討したほか，結晶の構造特性が熱電性能に及ぼす影響を，電子状態計算に基づき考察した．本研究から得られた知見は，熱電材料の高性能化にむけた重要な示唆を与えるものである．