Hydrothermal synthesis and properties of terbium- or praseodymium-doped Ce1-xSmxO2-x/2 solid solutions

The structure, thermal expansion coefficients and ionic conductivity of (Ce0.83Sm0.17)(1-x)(Tb/Pr)(x)O1.915+delta (x = 0-0.10) solid electrolytes prepared hydrothermally were investigated. The uniformly small particle size (7-14 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1400 degrees C, a significantly lower temperature, compared to that at 1600-1650 degrees C required for samples prepared by solid state techniques. The maximum conductivity was found at x = 0.10 for the Pr- and Tb-substituted ceria (sigma(600 degrees C) = 7.6 x 10(-3) S/cm, E-a = 0.55 eV and sigma(600 degrees C) = 10(-2) S/cm, E-a = 0.72 eV, respectively) with electronic contribution to the total conductivity around 20-30%. When the Tb or Pr substitution in Ce0.83Sm0.17O1.915 is reduced, the conductivity becomes more ionic, and is purely ionic at 2% of Tb or Pr. However the conductivity at this lower level of doping is not significantly lower (e.g. sigma(600 degrees C) = 5.6 x 10(-3) S/cm for Tb). The thermal expansion coefficients, determined from high-temperature X-ray data, are 8.6 x 10(-6) K-1 for the Ce0.83Sm0.17O1.915 and slowly increase with increasing Pr substitution and decrease with increasing Tb substitution. (C) 1998 Published by Elsevier Science B.V. All rights reserved.