Low-temperature densification and grain growth of Bi2O3-doped-ceria gadolinia ceramics

The effect of small amounts (≤ 2.0 wt.%) of Bi2O3 on the sintering characteristics and grain growth of cerium oxide doped with gadolinium oxide has been evaluated. The temperature of the shrinkage-rate maximum decreased by almost 300 °C in the case of the doped gadolinia-modified ceria, (GDC) containing 2.0 wt.% Bi2O3. An apparent density > 99% of the theoretical density (Dth) has been achieved on sintering at 1400 °C for 4 h for GDC containing 1.0 wt.% Bi2O3 and of the order of 97.9% on sintering for 2 h for GDC containing 0.5 wt.% Bi2O3. The grain growth kinetics have been studied in terms of the kinetic grain growth equation: Dn = Kot exp (−Q/RT) for sintering in air from 1400° to 1550 °C. The apparent activation energy for the grain growth of GDC increased to about 892 KJ/mol from 518 KJ/mol for undoped-GDC. This result may indicate that additions of Bi2O3 retard the grain growth of GDC ceramics. The conductivity of 1 wt.% doped samples has been measured by complex impedance spectroscopy (CIS). Doping with Bi2O3 does not modify the conductivity of the GDC solid solution.