Yazar "Nishino, Yoichi" seçeneğine göre listele

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    Öğe
    Local Structure of Heusler-Type Fe2V1-XTaXAl Thermoelectric Materials Studied by X-Ray Absorption Fine-Structure Spectroscopy
    (Wiley-V C H Verlag Gmbh, 2022) Takahashi, Kouki; Miyazaki, Hidetoshi; Kimura, Koji; Ozkendir, Osman Murat; Nishino, Yoichi; Hayashi, Kouichi
    The local structure around doping Ta atoms in Fe2V1-xTaxAl alloys is investigated using X-ray absorption fine-structure (XAFS) and synchrotron radiation X-ray diffraction (SR-XRD) measurements to elucidate the origin of the reduction in their thermal conductivity. XAFS and SR-XRD results show that with the substitution of Ta atoms at the V site, local strain exists around the doped Ta atoms. The reduction in the thermal conductivity due to Ta doping in the Fe2V1-xTaxAl alloys is attributed to the increase in the average atomic mass substituted with the heavy element Ta as well as the existence of the local strain.
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    Machine learning based prediction of lattice thermal conductivity for half-Heusler compounds using atomic information
    (Nature Portfolio, 2021) Miyazaki, Hidetoshi; Tamura, Tomoyuki; Mikami, Masashi; Watanabe, Kosuke; Ide, Naoki; Ozkendir, Osman Murat; Nishino, Yoichi
    Half-Heusler compound has drawn attention in a variety of fields as a candidate material for thermoelectric energy conversion and spintronics technology. When the half-Heusler compound is incorporated into the device, the control of high lattice thermal conductivity owing to high crystal symmetry is a challenge for the thermal manager of the device. The calculation for the prediction of lattice thermal conductivity is an important physical parameter for controlling the thermal management of the device. We examined whether lattice thermal conductivity prediction by machine learning was possible on the basis of only the atomic information of constituent elements for thermal conductivity calculated by the density functional theory in various half-Heusler compounds. Consequently, we constructed a machine learning model, which can predict the lattice thermal conductivity with high accuracy from the information of only atomic radius and atomic mass of each site in the half-Heusler type crystal structure. Applying our results, the lattice thermal conductivity for an unknown half-Heusler compound can be immediately predicted. In the future, low-cost and short-time development of new functional materials can be realized, leading to breakthroughs in the search of novel functional materials.
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    Öğe
    Probing local distortion around structural defects in half-Heusler thermoelectric NiZrSn alloy
    (Nature Portfolio, 2020) Miyazaki, Hidetoshi; Ozkendir, Osman Murat; Gunaydin, Selen; Watanabe, Kosuke; Soda, Kazuo; Nishino, Yoichi
    The half-Heusler NiZrSn (NZS) alloy is particularly interesting owing to its excellent thermoelectric properties, mechanical strength, and oxidation resistance. However, the experimentally investigated thermal conductivity of half-Heusler NZS alloys shows discrepancies when compared to the theoretical predictions. This study investigates the crystal structure around atomic defects by comparing experimental and theoretical X-ray absorption fine structure (XAFS) spectra of the crystal structure of a half-Heusler NZS alloy. The results of both Zr and Ni K-edge XAFS spectra verified the existence of atomic defects at the vacancy sites distorting the C1(b)-type crystal structure. We concluded that the distortion of the atoms around the interstitial Ni disorder could be the probable reason for the observed lower thermal conductivity values compared to that predicted theoretically in half-Heusler alloys. Our study makes a significant contribution to the literature because the detailed investigation of the lattice distortion around atomic defects will pave the way to further reduce the thermal conductivity by controlling this distortion.