Phase Diagram and Oxygen-Ion Conductivity in the Y2O3-Nb2O5 System |
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| Authors: | Jin-Ho Lee Masatomo Yashima Masato Kakihana Masahiro Yoshimura |
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| Affiliation: | Materials and Structures Laboratory, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226, Japan;Department of Materials Science and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta 4259, Midori-ku, Yokohama 226, Japan |
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| Abstract: | The phase equilibria in the Y2O3-Nb2O5 system have been studied at temperatures of 1500° and 1700°C in the compositional region of 0-50 mol% Nb2O5. The solubility limits of the C-type Y2O3 cubic phase and the YNbO4 monoclinic phase are 2.5 (±1.0) mol% Nb2O5 and 0.2 (±0.4) mol% Y2O3, respectively, at 1700°C. The fluorite (F) single phase exists in the region of 20.1-27.7 mol% Nb2O5 at 1700°C, and in the region of 21.1-27.0 mol% Nb2O5 at 1500°C, respectively. Conductivity of the Y2O3- x mol% Nb2O5 system increases as the value of x increases, to a maximum at x = 20 in the compositional region of 0 ≤ x ≤ 20, as a result of the increase in the fraction of F phase. In the F single-phase region, the conductivity decreases in the region of 20-25 mol% Nb2O5, because of the decrease in the content of oxygen vacancies, whereas the conductivity at x = 27 is larger than that at x = 25. The conductivity decreases as the value of x increases in the region of 27.5 ≤ x ≤ 50, because of the decrease in the fraction of F. The 20 mol% Nb2O5 sample exhibits the highest conductivity and a very wide range of ionic domain, at least up to log p O2=?20 (where p O2 is given in units of atm), which indicates practical usefulness as an ionic conductor. |
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