Development of complex-cation engineering for high-performance thermoelectric oxides

2023 Fiscal Year Final Research Report

• Project/Area Number: 20H02443
• 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: Keio University
• Principal Investigator: Hagiwara Manabu 慶應義塾大学, 理工学部(矢上), 講師 (30706750)
• Project Period (FY): 2020-04-01 – 2024-03-31
• Keywords: 熱電変換材料 / セラミックス / 複合カチオン / ペロブスカイト

Outline of Final Research Achievements

In the present study, we adopted a method of replacing the Ca2+ and Sr2+ sites of perovskite-type oxides CaMnO3 and SrTiO3 with "complex cations" consisting of two cations with different valence, in order to reduce their thermal conductivity. For the CaMnO3-based system, replacing 10% of the Ca2+ sites with a complex cation consisting of Gd3+ and Na+ significantly reduced the thermal conductivity and gave a high power factor, resulting in a significant improvement in the dimensionless performance index ZT compared to pure CaMnO3. For (La1/2K1/2)TiO3, in which all of the Sr2+ in SrTiO3 is replaced by a complex cation consisting of La3+ and Na+, it was found that both high electrical conductivity and low thermal conductivity can be achieved by increasing the grain size.

Free Research Field

無機材料科学

Academic Significance and Societal Importance of the Research Achievements

これまでに酸化物熱電材料の熱伝導率を低減する手法として、主にはグレインの微細化や第二相との複合化によるフォノン散乱の増強が試みられてきたが、これらの”extrinsic”な効果は微細構造や組成のわずかな変化に強く影響されてしまうことが問題であった。本研究で実証した複合カチオンの導入による熱伝導率の低減は結晶化学に基づく”intrinsic”な効果であり、グレインサイズ等の微細構造の変化に依存しない。したがって本研究の成果は酸化物系熱電変換素子の実現に向けた材料設計の幅を大きく拡大することを可能とするものである。