Abstract: By means of XRD and XPS measurements, the structural characteristics and valence states of a series of nanocrystalline solid solutions(CeO₂)_1-x(BiO_1.5)_x(x =0.0～0.50) synthesized under mild hydrothermal conditions at 240 ℃ were investigated. The solution limit of Bi₂O₃in ceria is as high as ca . 50 %. XRD data showed that all solid solutions crystallized in single phase cubic fluorite type structure. This result is different from the solid state reaction routes. The average grain size of all solid solutions was within a narrower range of 10～18 nm. XPS data gave evidence of the presence of Bi(Ⅲ) and Ce(Ⅳ) in all doped ceria. When the content of dopant Bi₂O₃in ceria was lower than the limit, air firing of the as made doped ceria up to 800 ℃ did not lead to any structural transformation. For the solid solution of (CeO₂)_0.5(BiO_1.5)_0.5, sintering it in air at 800 ℃ would cause the limit exceeded as well as segregation of an unknown phase. The ionic conduction measured by impedance spectroscopy showed that the solid solutions with bismuth content lower than the limit exhibited only the bulk conduction. The bulk conduction of solution(CeO₂)_0.6(BiO_1.5)_0.4was due to oxide ions and the grain boundary to silver from the electrode.

Key words: Structural characteristics, Transport properties, Nanocrystalline