2015 年 123 巻 1437 号 p. 367-373
A series of (Gd2−xLix)Ti2O7−x with x = 0.050–0.150, abbreviated as GLT-2L were prepared by the addition of 2x mole of LiO0.5 self-flux in the parent compound. Preparation temperatures were between 1450 and 1500°C depending on the amount of the self-flux addition. Relative densities of all GLT-2L samples were larger than 97.9(3)%. However, the parent compound, Gd2Ti2O7 has no LiO0.5 co-existence, it has a relative density of 92.8(4)% only, although it was prepared at a higher temperature, 1650°C. Among the GLT-2L samples, the one with x = 0.110 has the highest total electrical conductivity, 6.17(6) × 10−5 S·cm−1 at 700°C and the lowest activation energy, 0.95(3) eV. Doping Li+ ions into the Gd-site of Gd2Ti2O7, preparation temperature was lowered and samples become denser. Meanwhile, vacancies were created and electrical conductivity was increased. At 500°C, average ionic transference numbers (ti) found for all samples are fully ionic. Increasing temperature, ti decreases slightly due to the increase of the fractional electronic conductivity of the (Gd2−xLix)Ti2O7−x, which is a mixed conductor at high temperature. Ti atoms are in the the mixed valence states.
