Published online by Cambridge University Press: 10 February 2011
The structure, thermal expansion coefficients and ionic/electronic conductivity of (Ce1−xSmx)1-y(Tb/Pr)yO2-x/2)+δ (x=0–0.30; y=0–0.10) and Ce1−xCaxO2-x ( x= 0–0.17) solid electrolytes prepared hydrothermally were investigated. The uniformly small particle size (7–68 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1400°C, a significantly lower temperature, compared to that at 1600–1650°C required for samples prepared by solid state techniques. The maximum ionic conductivity in Ce1−x(Sm/Ca)xO2-δ was found at x= 0.17 for the Sm (σ600°c = 5.7×10−3 S/cm). In (Ceo0.83Sm0.17)1-y(Tb/Pr)yO1.915+δ the maximum conductivity was found at y= 0.17 for the Pr and Tb substituted ceria (σ600°c=7.6x10−3S/cm, Ea= 0.55 eV and σ600°c = 10−2 S/cm, Ea= 0.72 eV respectively) with electronic contribution to total conductivity around 20–30 %. When the Tb or Pr substitution in Ce0.83Sm0.17OO1.915 is reduced, the conductivity becomes more ionic, and is purely ionic at 2 %. However the conductivity at this lower level doping is not significantly lower.