関根ちひろ(Chihiro Sekine)研究室

Japanese Journal of Applied Physics 58,081006 (2019)
これまでCoSb₃に充填する系の熱電材料の向上を行ってきましたが、今回RhSb₃にYbを高充填させることに成功しました。
その結果、Yb_0.27Rh₄Sb₁₂の組成で420 Kにおいて熱電性能指数ZT=0.1を記録しました。
Thermoelectric materials of Yb_xRh₄Sb₁₂ (0 ≤ x ≤ 0.8, nominal) were synthesized using a high-pressure apparatus (UHP-500, Sumitomo Heavy Industries Ltd., Japan) with the cubic anvil cell. Thermoelectric properties such as thermal conductivity, electrical resistivity and Seebeck coefficient were investigate at temperature 2-700K. The phase composition and the actual Yb filling ratio x of Yb_xRh₄Sb₁₂ were characterized by X-ray diffraction (XRD) and scanning electron microscope with energy-dispersive X-ray microanalyzer (EDX). The maximum actual Yb filling ratio x increases to 0.44, higher than any sample that prepared under ambient pressure. The electrical resistivity of filled Yb_xRh₄Sb₁₂ compound showed semiconducting behavior. The resistivity of filled skutterudite decrease with increasing lattice parameter and filling fraction. The Seebeck coefficient shows the negative value (n-type conductivity). The highest dimensionless figure of merit ZT was found to be 0.1 at 420K at Yb_0.27Rh₄Sb₁₂

高温高圧合成法により超伝導物質CaOs₄P₁₂を発見しました。
Physical Review B 98,024513 (2018)
室蘭工業大学学術資源アーカイブ
これまでカルシウム（Ca）系スクッテルダイト化合物は試料準備の難しさからあまり見つかっておらず、その中で私たちはCaOs₄P₁₂の合成に成功し、それが超伝導であることを発見しました。大気圧の4万倍の圧力、1050℃の温度の下での高温高圧合成法により合成できました。

 

High-pressure and high-temperature synthesis made a calcium based filled skutterudite superconductor possible. Among filled skutterudites AT₄X₁₂ showing high thermoelectric performance or unique electrical transport and magnetic properties by the combination of elements, few of calcium based filled skutterudites CaT₄X₁₂ have been found. We have discovered the first calcium based filled skutterudite superconductor CaOs₄P₁₂. It is enabled at the condition of high-pressure and high-temperature with 40,000 atmospheres and 〜1300 Kelvin under oxygen-free environment. Thermodynamic, electrical transport, magnetic properties of CaOs4P12 indicate that CaOs₄P₁₂ is an intrinsic bulk superconductor below 2.5 Kelvin.