Creation of High Performance Thermoelectric Materials by Synthesis of Novel Cobalt Layered Compounds with Low Thermal Conductivity and Its Sintering

2022 Fiscal Year Final Research Report

• Project/Area Number: 18K14031
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 26050:Material processing and microstructure control-related
• Research Institution: Kanagawa Institute of Technology (2022); Ube National College of Technology (2018-2021)
• Principal Investigator: SHIGENO Koichi 神奈川工科大学, 工学部, 教授 (60707131)
• Project Period (FY): 2018-04-01 – 2023-03-31
• Keywords: 熱電材料 / コバルト層状化合物 / セラミックス / 酸化剤 / 緻密化

Outline of Final Research Achievements

We synthesized the Co-layered compound with a narrower interlayer distance than a starting material powder, NCO (NaxCoO2) having the highest level of thermoelectric performance as an oxide using a simple soft chemical process, the oxidation-reduction method. However, the above compound was not thermally stable and decomposed at around 300°C. Therefore, in this study, we examined densification by the hydrothermal hot pressing (HHP) method, in which a small amount of aqueous solution is added to the powder, and then pressurized and heated. As a result, a dense sintered body with a relative density exceeding 80 % could be produced at 250 °C, which is an ultra-low temperature as an oxide. Although we could not obtain good thermoelectric properties, we found the possibility of the HHP method as one of the methods to densify thermoelectric materials such as the above-mentioned Co-layered compounds that are not thermally stable.

Free Research Field

材料工学

Academic Significance and Societal Importance of the Research Achievements

本研究成果における学術的意義は、本研究で用いたCo層状化合物などの熱安定性のない熱電物質を緻密化する手法の1つとして水熱ホットプレス法の可能性を見出すことができた点にある。今後、低温での緻密化メカニズム解明を行ううえでの基礎となるデータが得られたものと考えられる。
本研究成果における社会的意義は、本手法が省エネルギー化に直接貢献するとともに、今後における焼成条件や助剤の改良により、高性能な機能性材料の開発が期待される点にある。