A new approach to improve the grain-boundary conduction in 10 mol% gadolinia-doped ceria (GDC) without any additives was suggested. The grain-boundary conductivity of GDC specimen containing 500 ppm of SiO2 was increased similar to 4 times by post-sintering heat-treatment (HT) at 1350 degrees C for 20 h. The grain-boundary conductivity showed the maximum at HT temperature of 1350 degrees C and enhanced with increasing HT time from 0 to 20 h. The mechanism for scavenging resistive siliceous phase by post-sintering HT was investigated with the variation of HT temperatures, HT times, and HT schedules. (c) 2005 Elsevier B.V. All rights reserved.