Phase equilibria in this system were studied, at temperatures of 1500 and 1700C, for compositions ranging from 0 to 50mol%Nb2O5. The solubility limits of the C-type Y2O3 cubic phase and the YNbO4 monoclinic phase at 1700C were 2.5mol%Nb2O5 and 0.2mol%Y2O3, respectively. The fluorite single phase existed between 20.1 and 27.7mol%Nb2O5 at 1700C, and between 21.1 and 27.0mol%Nb2O5 at 1500C. The conductivity of the system increased, as the Nb2O5 content was increased, up to a maximum at 20mol%Nb2O5. This was due to an increase in the fraction of fluorite phase. In the fluorite single-phase region, the conductivity decreased between 20 and 25mol%Nb2O5. This was because of a decrease in the content of O vacancies. The conductivity at 27mol%Nb2O5 was higher than that at 25mol%Nb2O5. The conductivity decreased, between 27.5 and 50mol%Nb2O5, because of a decrease in the fraction of the fluorite phase. A 20mol%Nb2O5 sample exhibited the highest conductivity.

J.H.Lee, M.Yashima, M.Kakihana, M.Yoshimura: Journal of the American Ceramic Society, 1998, 81[4], 894-900