Ce0.8Gd0.2O19 (CGO) and Ce0.8Sm0.2O19 (CSO) have been prepared as polycrystalline materials using a freeze-dried precursor. This method yields amorphous nanometric powders. Crystallization of the fluorite phase occurred on heating at 600 degreesC or higher temperatures. The grain size of freeze-dried powders increases to about 100 nm after calcination at 800 degreesC, or about 200 nm after firing at 1000 degreesC. Freeze-dried powders were used to prepare dense ceramic disks by sintering at 1400 degreesC. Some disks were sintered at 1000 degreesC by adding small amounts of cobalt nitrate solution to assist the densification. The electrical conductivity results obtained for these gadolinia-doped ceria and samaria-doped ceria ceramics are similar to those obtained for CGO pellets obtained from commercial nanopowders (Rhodia). Though the bulk conductivity of CSO is probably higher than that of CGO, its grain boundary conductivity is inferior, and tends to control the overall behaviour, at least at relatively low temperatures. (C) 2003 Elsevier Science Ltd. All rights reserved.