Effect of CaO concentration on enhancement of grain-boundary conduction in gadolinia-doped ceria

This study examines the effect of calcium oxide (CaO) addition to Ce0.9Gd0.1 O-1.95 (gadolinia-doped ceria, CDC) containing 500 ppm SiO2 on grain-interior and grain-bounclary conduction. The CDC can be used as a solid electrolyte for intermediate and low-temperature solid oxide fuel cells. Doping with >= 2 mol% CaO results in a decrease in apparent grain-boundary resistivity at 300 degrees C from 746.7 k Omega cm to 2.8-3.5 k Omega cm. The total resistivity exhibits a minimum at 2 mol% CaO. Further increase in CaO concentration to 10 mol% results in an increase in grain-interior resistivity from 3.1 to 40 k Omega cm. Although most of the CaO is incorporated into the GDC lattice, a small amount of CaO scavenges the intergranular siliceous phase, which leads to a significant increase in grain-bounclary conduction. The increase in grain-interior resistivity at high CaO concentration is attributed to defect association between Vo center dot center dot and Ca-ce. (C) 2008 Elsevier B.V. All rights reserved.