Development of high-performance thermoelectric materials using impurity states formed near the band edge

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01628
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 26020:Inorganic materials and properties-related
• Research Institution: Toyota Technological Institute
• Principal Investigator: Takeuchi Tsunehiro 豊田工業大学, 工学(系)研究科(研究院), 教授 (00293655)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 熱電材料 / ゼーベック係数 / 電気伝導度 / 熱伝導度 / 出力因子 / 熱電無次元性能指数 / スペクトル伝導度 / 不純物順位

Outline of Final Research Achievements

By employing impurity states near the band edge of thermoelectric semiconductors, we tried to improve their thermoelectric performance. This concept allows us to simultaneously obtain a large magnitude of Seebeck coefficient and rather small electrical resistivity.
Fe 3d impurity states are introduced in the conduction band of Si-Ge alloys. With the help of nano-structuring leading to a reduction in lattice thermal conductivity, the observed ZT exceeded 3. This strategy also applied to Ag2S1-xSex, that is characterized by extremely small lattice thermal conductivity due to anharmonic lattice vibrations. The intentionally introduced V 3d states near the bottom of conduction band led to a significant increase of Seebeck coefficient with keeping its electrical resistivity unchanged.
We revealed that this strategy works only when the electrons stays in the strongest scattering limit, and also the potential of the proposed strategy in developing high-performance thermoelectric materials.

Free Research Field

金属電子論，半導体電子論，熱電物性

Academic Significance and Societal Importance of the Research Achievements

熱電材料を開発するためにはゼーベック係数，電気伝導度，熱伝導度を同時に最適化する必要があるが，これらの物性は相関しているために，建設的に材料設計することが難しいと言われてきた．本研究では，ゼーベック係数．電気伝導度，および電子熱伝導度を同時に最適化する方法を提案し，それを証明した．さらに，格子熱伝導度を同時に低減する手法の提案と証明も行っており，新しい考え方を提示している点において学術的価値が高い．結果として得られる材料は．実用化材料の性能を上回っていることから，工学的に意義が高いと判断される．さらに，結果として得られる素子は，省エネルギー社会の構築に資するため，社会的な意義も有している．