Enhancement of grain-boundary conduction in gadolinia-doped ceria by the scavenging of highly resistive siliceous phase

This paper proposes MgO as a new scavenger material that can mitigate the harmful effects of SiO2 impurity on the grain-boundary conduction in 10 mol.% gadolinia-doped ceria (GDC). The addition of 0.3–10 mol.% of MgO resulted in an up to ∼45-fold increase in the grain-boundary conduction of a GDC specimen containing 500 ppm of SiO2 impurity. The solubility limit of MgO in GDC was found to be as low as ∼0.1 mol.% and most of the MgO existed as a second phase. Electron energy-loss spectroscopic analysis indicated the formation of forsterite (Mg2SiO4), due to a reaction between MgO and the siliceous intergranular phase, to be the scavenging mechanism.