The electrical conductivity of Ce0.992Nb0.008O2−δ was measured as a function of O partial pressure between 10−28 and 1bar, at 873 to 1173K. The activation energy for the conductivity at an O partial pressure of 10−4 bar was 0.29eV. This value was too small to be assigned to oxide ion conduction, indicating that, in oxidizing atmospheres, electronic conduction was dominant due to Nb doping. On the other hand, the O partial pressure dependence of conductivity was complicated in reducing atmospheres. Defect chemical analysis was made to interpret the conductivity variation with O partial pressure. The defect association model was introduced, which assumed that O vacancies were easily formed around Nb ions and that one of the released electrons was trapped on Nb5+. The experimental data was found in accordance with that calculated by the proposed defect association model.

Electrical Properties and Defect Structure of Niobia-Doped Ceria. K.Yashiro, T.Suzuki, A.Kaimai, H.Matsumoto, Y.Nigara, T.Kawada, J.Mizusaki, J.Sfeir, J.Van herle: Solid State Ionics, 2004, 175[1-4], 341-4