Takayuki Nagai
Mitsubishi Electric
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Publication
Featured researches published by Takayuki Nagai.
Japanese Journal of Applied Physics | 2013
Yoshiharu Enta; Kano Ogawa; Takayuki Nagai
We investigate the thermal decomposition of 20-nm-thick silicon oxide layers on Si(100) at a temperature of 1050 °C in vacuum by X-ray photoelectron spectroscopy, scanning Auger electron microscopy, and atomic force microscopy. Time evolutions of chemical-shift components in Si 2p core-level spectra are analyzed with the SiO2-decomposition model based on void formation. The experimental data can be reproduced well if the void area is proportional to the square of the annealing time, being consistent with the model in which the reaction at the void periphery is the rate-limiting step for void growth. Microscopic images show that the void periphery is square with rounded corners, and many silicon nanostructures are formed inside the void. These observations reflect reaction processes of the thermal decomposition of the silicon oxide layer.
IEEE Transactions on Applied Superconductivity | 2006
Yoshio Kubo; Kunihiko Egawa; Takayuki Nagai; Takanori Sone; Bunko Ikeda; Mitsuru Hasegawa; M. Kosuge
An internal-tin route Nb<sub>3</sub>Sn superconducting wire that has both remarkably low hysteresis loss (Q<sub>h</sub>) and high critical current density (J<sub>c</sub>) was developed according to a new design idea. The wire was constructed by arranging the filaments in a radial layout, enlarging the outer filaments along the radial direction, intentionally narrowing the filament spacing in the radial direction, and enlarging the filament spacing in the tangential direction. Thus, the electromagnetic coupling among the filaments in the tangential direction due to the bridging and/or proximity effect was suppressed without decreasing the volume fraction of Nb. As a result, excellent properties such as J<sub>c</sub>(12 T)=1.15times10<sup>3 </sup> A/mm<sup>2</sup> Q<sub>h</sub>=301 mJ/cm<sup>3</sup> (for 1 cycle of B=plusmn3 T), T<sub>c</sub>=17.3 K, and B<sub>c2</sub>=24.1 T were obtained. Scanning electron microscope observations confirmed that the cause of experimental Q<sub>h</sub> values being lower than expected is that the majority of the filaments in the second and outermost rows were not completely combined. Electron probe micro-analyses confirmed that the good T<sub>c</sub> and B<sub>c2</sub> values resulted from the qualitative improvement of the Nb<sub>3</sub>Sn compound. This wire is promising for use with conduction-cooled high-field magnets and for the strands of fusion coils
Japanese Journal of Applied Physics | 1987
Mitsunobu Wakata; F. Fujiwara; Yoshio Kubo; Shoji Miyashita; Shigeru Matsuno; Takayuki Nagai; Hiroko Higuma; Kiyoshi Yoshizaki; Masao Morita; Shoichi Yokoyama; Shunji Yamamoto; Tadatoshi Yamada
Superconducting oxides, La–Sr–Cu–O and Y–Ba–Cu–O were prepared using nitrate mixture by spray dry method and/or oxide and carbonate powder mixtures followed by pressing and sintering. The superconducting properties such as critical temperature (Tc) and critical current density (Jc) were measured by resistive and inductive methods, and transport current and magnetization measurements, respectively. The Tcs(the resistive offset) were 32, 91 K for La and Y system, respectively. The Jc(77K) of 1,840 A/cm2 was observed for Y system by transport current measurement.
Japanese Journal of Applied Physics | 1987
Tadatoshi Yamada; Masao Morita; Shoichi Yokoyama; Shunji Yamamoto; Masatami Iwamoto; Kiyoshi Yoshizaki; Mitsunobu Wakata; Fumio Hujiwara; Yoshio Kubo; Shoji Miyashita; Shigeru Matsuno; Takayuki Nagai; Yasuo Hashimoto
The bulk specimens of (Y1-xBax)3Cu3O8-δ, x=0.5~0.73 were prepared from oxide and carbonate powder mixtures. Critical temperature was higher than 90 K in the four-probe method. Critical current, 113 A/cm2 was also obtained in the same method at liquid nitrogen temperature and zero external field. Persistent current was proved at liquid nitrogen temperature.
Archive | 2004
Takefumi Ito; Yuujitsushi Iwashita; Toshikazu Kawabata; Toshihiro Kurita; Takayuki Nagai; 武文 伊藤; 由実子 岩下; 俊和 川畑; 敏広 栗田; 貴之 永井
Archive | 2007
Takefumi Ito; Toshikazu Kawahata; Yumiko Iwashita; Toshihiro Kurita; Takayuki Nagai
Journal of Cryogenics and Superconductivity Society of Japan | 1996
Yoshio Kubo; Kunihiko Egawa; Takayuki Nagai; Fusaoki Uchikawa; Osamu Taguchi; Masao Morita
Journal of Cryogenics and Superconductivity Society of Japan | 1996
Yoshio Kubo; Kunihiko Egawa; Takayuki Nagai; Fusaoki Uchikawa; Osamu Taguchi; Masao Morita
Cryogenics | 2006
Yoshio Kubo; Kunihiko Egawa; Takayuki Nagai; Takanori Sone; Bunko Ikeda; Mitsuru Hasegawa; M. Kosuge
Journal of Cryogenics and Superconductivity Society of Japan | 2005
Yoshio Kubo; Kunihiko Egawa; Takayuki Nagai; Takanori Sone; Bunko Ikeda; Mitsuru Hasegawa; M. Kosuge