Two series of samples, Sm2Zr2O7 and Eu2Zr2O7, were prepared by the polymeric citrate precursor method and calcined in static air between 7001450˚C for 24 h. Nano-size particles obtained were larger with increasing calcination temperatures. Sm2Zr2O7 and Eu2Zr2O7 samples have fluorite phase if they are prepared at temperatures lower than 1000 and 1100˚C, respectively. On the other hand, if the samples are prepared at temperatures higher than 1100 and 1150˚C, they have pyrochlore phase. Phase transition temperature depends on the ionic radius ratio of R(Ln3+)/R(Zr4+). The larger the ratio, the lower the transformation temperature is. Quenched samples have unit cell a-axis increases with increasing preparation temperatures. The amount of cation antisite in the disordered pyrochlore phase decreases with increasing calcination temperatures. Activation energies calculated on the log (σ‧T) vs. (1/T) for the Sm2Zr2O7 and Eu2Zr2O7 on the cation ordering process are 0.30(1) and 0.39(2) eV, and on the O(3) site are 0.70(9) and 1.2(2) eV, respectively. O2 is much bigger than R3+ so that more energy is required to overcome the hopping potential. Activation energy increases as the ionic radius ratio of theR(Ln3+)/R(Zr3+) decreases due to the decreasing of the unit cell volume.
Journal of the Chinese Chemical Society=中國化學會會誌 57(4)pt.B, pp.925-931