Synthesis of fine-structured CaB6 using nano crystals grown by low-temperature process for improvement of its thermoelectric properties

Research Project

Project/Area Number	18K04680
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Review Section	Basic Section 26010:Metallic material properties-related
Research Institution	Nagaoka University of Technology
Principal Investigator	TAKEDA Masatoshi 長岡技術科学大学, 工学研究科, 教授 (30293252)
Project Period (FY)	2018-04-01 – 2021-03-31
Project Status	Completed (Fiscal Year 2020)
Budget Amount *help	¥4,420,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥1,020,000) Fiscal Year 2020: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000) Fiscal Year 2019: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000) Fiscal Year 2018: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000)
Keywords	熱電変換材料 / 金属六ホウ化物 / ナノ結晶 / 微細組織 / 複合組織
Outline of Final Research Achievements	SrB6 sintered body with fine microstructure was fabricated using nanocrystalline powder to improve thermoelectric property by reducing its thermal conductivity. Nanocrystalline SrB6 was synthesized by the following two method: low-temperature synthesis using SrCl2 and NaBH4 as starting materials, and magnesium reduction of oxides. Dense sintered bodies were obtained at lower temperature than conventional method. Thermal conductivity was successfully reduced by 34% - 54%. The specimen fabricated using the magnesium reduced SrB6 exhibited high electrical properties comparable to those of conventional ones. Further improvement is expected by controlling carrier concentration.
Academic Significance and Societal Importance of the Research Achievements	低温合成された金属六ホウ化物のナノ結晶を用いることで，従来は焼結に1800℃以上の温度が必要であったが，本研究では1200℃ー1600℃まで温度を下げても緻密な焼結体が得られることが明らかになった．焼結温度の低温度化により，微細な組織を持つ焼結体が得られ，熱伝導率を低減できることが明らかになった．この成果は，ホウ素化合物において電気的特性と熱的特性を独立に制御可能であることを示しており，更なる熱電特性向上が期待される．また，高性能な熱電材料の開発は，排熱利用発電などエネルギーの有効活用に貢献するものである．