Ionic conductivity and relaxations of In-doped GDC (gadolinium doped ceria) ceramics

The effect of In doping on the sintering behaviors and electrical properties of Gd0.1Ce0.9O1.95 (Gd-doped ceria, or GDC) was investigated. The solubility limit of In in GDC was determined to be ~2 at%, and the lattice parameter of GDC was found to decrease from 5.417(7) Å to 5.416(5) Å with 2 at% In dopant. The mean grain size of the sintered body decreased with increasing In content. The concentration of In did not significantly affect the conductivity of the samples; however, undoped GDC showed the highest conductivity. Cole-Cole plots showed that the activation energies of the grain boundaries and grain interiors decreased and increased, respectively, as the In concentration increased to 1 at%. The decreased grain-boundary activation energy is attributed to the segregation of the negatively charged dopant at the grain boundaries, while the increased activation energy of the grain interiors is attributed to the decreases in both the lattice parameters and binding energies with In doping.