Abstract
A Gd-doped ceria powder (GDC, Ce0.8Gd0.2O1.9) prepared from an oxalate precursor was hot-pressed at 1173-1273 K in Ar atmosphere and annealed in air at 1273-1473 K to control the bulk density and grain size. Complex impedance of GDC of the microstructures of 0.29-5.6 μm average grain size and 95-98% theoretical density were measured at 573-1073 K in air in the frequency range from 100 Hz to 2 MHz. The bulk conductivity (σi(b)) was independent of the grain size and the activation energy for the migration of oxide ions was 85-88 kJ/mol. The grain boundary conductivity (σi(g)) was far small as compare with σi(b) (σi(g)=1/40-1/700 of σi(b) at 573 K). The σi(g) was influenced by the average grain size and showed a minimum value at around 3 μm and gradually increased with decreasing grain size. However, the total conductivity decreased for smaller grain size because of the increased thickness of grain boundary of relatively low conductivity. The information of diffusion of oxide ions from the surface into GDC inside was also reported.
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