Site Occupancies of Hydrogen in Nb Alloyed with Oversized Ta Atoms or Undersized Mo Atoms
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概要
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Site occupancies of hydrogen in Nb alloyed with 2 or 5 at. % of oversized Ta atoms have been investigated at room temperature for hydrogen concentrations of 0.01 and 0.029 at the hydrogen-to-metal-atom ratio (C_{\text{H}}=[\text{H}]/[\text{M}]), Nb0.98Ta0.02H0.01, Nb0.98Ta0.02H0.029, and Nb0.95Ta0.05H0.01, by the channelling method utilizing a nuclear reaction 1H(11B,\alpha)8Be with a 11B beam of about 2 MeV. It has been clearly demonstrated that hydrogen occupies also tetrahedral (T) sites, in addition to the displaced T sites (d-T sites), which were observed at higher hydrogen concentrations in the Nb0.95Ta0.05 alloys. The d-T site is a site displaced from a T site by about 0.25 Å towards its nearest neighbour octahedral (O) site. The T site is more favourable, but the concentration of available T sites is limited, and excess H atoms occupy the d-T sites. This site occupancy is different from that in Nb alloyed with similar concentration of undersized Mo atoms, where hydrogen preferentially occupies trapped sites T_{\text{tr}} displaced from T sites attached to Mo atoms by about 0.6 Å towards the Mo atoms due to a strong attractive interaction between them, but the concentration of T_{\text{tr}} sites is limited and excess H atoms enter T sites. On the other hand, there exists no such a strong attractive interaction between hydrogen and an oversized Ta atom. With the help of measurements of the half-widths of X-ray reflection lines in Nb--Mo and Nb--Ta alloys, the site occupancy of hydrogen in the Nb--Ta alloys is explained in terms of an effect of lattice distortion, which was induced by alloying with solute atoms, as in the case of the site occupancy in the Nb--Mo alloys at higher Mo concentrations than about 40 at. %. The d-T site is a stable site for hydrogen in a slightly distorted bcc lattice.
- 2011-10-15
著者
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SHISHIDO Toetsu
Institute for Materials Research (IMR), Tohoku University
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Murakami Yoichi
The School Of Science And Engineering Waseda University
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IIDA Takashi
the Second Department of Internal Medicine, Yamanashi Medical University
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Koike Shigetoshi
Department Of Physics Faculty Of Science Science University Of Tokyo
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YAGI Eiichi
RIKEN (The Institute of Physical and Chemical Research), Nishina Centre
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Sugi Chika
The School Of Science And Engineering Waseda University
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Hayashi Tatuya
The School Of Science And Engineering Waseda University
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Sugawara Takamasa
Institute For Materials Research (imr) Tohoku University
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Hirabayashi Kazuhiro
The School Of Science And Engineering Waseda University
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Okada Yoshinori
The School Of Science And Engineering Waseda University
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Yoshida Toru
The School Of Science And Engineering Waseda University
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Takebayashi Akiko
The School Of Science And Engineering Waseda University
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Ogiwara Kiyoshi
Riken (the Institute Of Physical And Chemical Research)
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Higami Naota
The School Of Science And Engineering Waseda University
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Yoshida Toru
The School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan
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Matsuba Hiroshi
RIKEN Nishina Centre for Accelerator-Based Science, Wako, Saitama 351-0198, Japan
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Higami Naota
The School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan
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Sugawara Takamasa
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
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Shishido Toetsu
Institute for Materials Reseach, Tohoku University, 2-1-1 Katahira-cho, Aoba-ku, Sendai 980-8577, Japan
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Hayashi Tatuya
The School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan
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Sugi Chika
The School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan
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Takebayashi Akiko
The School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan
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Iida Takashi
The School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan
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Okada Yoshinori
The School of Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan
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