An understanding of high-temperature aging effects on the electrical properties of electrolytes was very important in selecting optimum compositions for practical applications. The aging behavior and mechanisms of doped zirconia ceramics were extensively studied. However, little information was available regarding the aging behavior of ceria-based electrolytes. The present study demonstrated that a high-temperature aging (1000C) had a significant effect upon the ionic conductivity of the Y- or Gd-doped ceria (Ce1−xYxO2−δ and Ce1−xGdxO2−δ), especially in the case of the Gd doping. The aging behavior was characterized by a critical dopant concentration, above which the aging had a detrimental effect on the conductivity of the doped ceria ceramics. The aging behavior in the doped ceria cannot be explained by using the aging mechanisms applied to the doped zirconia. Instead, the formation of the microdomains in the doped ceria was acknowledged to be the main contribution to the aging behavior of the Y- or Gd-doped ceria ceramics. The formation ability of microdomains was estimated to be in the order of La3+>Gd3+>Y3+, based on the degree of size mismatch between the dopant ion and Ce4+ ion. The critical dopant concentrations at which the microdomains start to form for La3+, Gd3+ and Y3+ in the doped ceria ceramics were x=~0.15, ~0.2 and ~0.25, respectively. This critical dopant concentration was also an important indication: below which the conductivity was governed by only the association enthalpy, and above which the conductivity was dominated mainly by the microdomains rather than the association enthalpy.

Aging Behavior and Ionic Conductivity of Ceria-Based Ceramics - a Comparative Study. T.S.Zhang, J.Ma, L.B.Kong, S.H.Chan, J.A.Kilner: Solid State Ionics, 2004, 170[3-4], 209-17