受賞区分：出版社・新聞社・財団等の賞  受賞国：日本国

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACS Applied Energy Materials  

A type-I clathrate Ba8CuxSiyGe46-x-y ingot consisting of millimeter-sized grains with different crystallographic orientations was synthesized by the Czochralski method. The lower part of the ingot contained more Cu and Ge within the clathrate phase. The electrical resistivities of the top, middle, and bottom of the ingot at 550 °C were 0.78, 1.72, and 1.55 mΩ·cm, respectively. The differences in these values are consistent with the carrier concentration and calculated anisotropic effective mass of the electrons, which are based on the actual chemical composition and crystal orientation, respectively. The resistivity of the top part with few grain boundaries is less than a quarter of that of the hot-pressed sample with a similar composition. Despite the different carrier concentrations, the Seebeck coefficient of all parts had similar values of approximately −120 μV/K at 550 °C. The thermal conductivity at 350 °C was approximately 3.0 W/m·K for top part and 2.5 W/m·K for middle and bottom parts, about 1.5-1.8 times larger than those of previous reported hot-pressed samples. The power factor and dimensionless figure of merit ZT value of the top reached 18.8 μW/cm·K2 and 0.34, respectively. These results indicate that fabrication by the Czochralski method can improve the thermoelectric performance of Ba8CuxSiyGe46-x-y clathrates.

DOI： 10.1021/acsaem.3c02961

Web of Science

Scopus

担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

A two-layer bulk Si material with different boron concentrations was prepared using spark plasma sintering to improve its thermoelectric performance by blocking minority carrier diffusion across its interfaces. The sintered two-layer sample (p+/p-Si) was cut to include the interface. Two monolayer samples (p+-Si, p-Si) were prepared for comparison. Seebeck coefficient mapping of the p+/p-Si surface by thermal probing confirmed a Seebeck coefficient gap between the two p-type Si layers, indicating that a band offset exists at the interface. When compared with the average resistivities and voltages for p+-Si and p-Si, the electrical resistivity in the p+/p-Si sample is almost identical, but the thermoelectric voltage is higher when the p+-part is heated more than the p-part. This indicates that bipolar carrier transport inhibition in the band offset improved the thermoelectric voltage. This bandgap engineering process and principle can be extended to other thermoelectric materials that can be processed via powder sintering.

DOI： 10.35848/1347-4065/ace4af

Web of Science

Scopus

その他リンク： https://iopscience.iop.org/article/10.35848/1347-4065/ace4af/pdf

担当区分：責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：傾斜機能材料研究会  

<p>Chromium disilicide (CrSi₂) is generally known as a p-type degenerate semiconductor whose power factor can be improved by substitution of Al on the Si site. However, it has not been clarified why holes are majority carriers in pure CrSi₂ nor how the thermoelectric properties of CrSi₂₋<i>_x</i>Al<i>_x</i> depend on the temperature above 400 °C. In this paper, we prepared CrSi₂₋<i>_x</i>Al<i>_x</i> samples with <i>x</i> ranging from 0.00 to 0.20. The composition ratio in each sample measured by Wavelength-dispersive X-ray spectroscopy (WDX) showed that the sum of Si and Al to Cr was less than the stoichiometric ratio. The electronic density of states calculated by first principles calculation based on density functional theory revealed that the atomic vacancies on the Si sites, whose existence was implied by WDX, can supply holes. Comparing thermoelectric properties of the samples at 500 °C, the sample with nominal composition CrSi_1.96Al_0.04 showed the highest power factor 0.606 mW m⁻¹ K⁻².</p>

DOI： 10.14957/fgms.36.13

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1021/acs.inorgchem.2c01439

Web of Science

PubMed

記述言語：英語   出版者・発行元：傾斜機能材料研究会  

<p>A series of single crystalline Ba₈Cu<i>_x</i>Si_46-<i>_x</i> clathrate semiconductors with different Cu contents were successfully fabricated via Czochralski (CZ) method. The actual Cu content can increase with nominal Cu ratio, resulting in the higher values of Seebeck coefficient and electrical resistivity. Among the series, Ba_7.89Cu_4.66Si_41.34 sample shows a relatively high power factor of 0.688 mW/K² m at 500 °C. These results support that control of the Cu content leads to improvement of the power factor in Ba₈Cu<i>_x</i>Si_46-<i>_x</i> clathrate thermoelectric materials.</p>

DOI： 10.14957/fgms.35.8

CiNii Research

総ページ数：420   記述言語：日本語 著書種別：学術書

開催年月日： 2024年2月

会議種別：口頭発表（招待・特別）  

開催年月日： 2022年10月

記述言語：日本語  

開催地：長崎県壱岐市   国名：日本国  

開催年月日： 2024年3月

会議種別：口頭発表（一般）  

開催年月日： 2024年3月

会議種別：口頭発表（一般）  

開催年月日： 2024年3月

会議種別：口頭発表（一般）  

対象： 高校生

種別：講演会

女性研究者の研究活動紹介、質疑応答

対象： 高校生

種別：施設一般公開

大学生活や研究活動について紹介すると共に、熱電材料についてのデモ実験や設備の解説を行った。

対象： 大学生,　大学院生,　教育関係者,　研究者,　社会人・一般

種別：その他

学生時代の研究活動・研究室生活の経験に基づいて、後輩にあたる大学生・大学院生に向けての助言・勧めを含んだ講演を行った。また学内外からの参加者向けに、現在の研究活動の一端も紹介した。