We report on ac conductivity measurements of oxide ion conductors with composition ${\text{Gd}}_2{\left({\text{Zr}}_y{\text{Ti}}_{1-y}\right)}_2{\text{O}}_7$, at temperatures between 170 and 500 K and in the frequency range 1 Hz–3 MHz, and show that a crossover from a sublinear power law to a linear frequency dependence (or nearly constant loss behavior) in the ac conductivity can be clearly observed in a wide temperature range. This crossover is found to be thermally activated, and its activation energy $E_{\text{NCL}}$ to be much lower than the activation energy $E_{\text{dc}}$ for the dc conductivity. We also found that the values of $E_{\text{NCL}}$ are almost independent of composition, and therefore of the concentration of mobile oxygen vacancies, unlike those of $E_{\text{dc}}$. Moreover, for each composition, the values of $E_{\text{NCL}}=0.67\pm 0.04$ are very similar to those estimated for the energy barrier for the ions to leave their cages, $E_a=0.69\pm 0.05$. These results support that the nearly constant loss behavior, ubiquitous in ionic conductors, is originated from caged ion dynamics.

• Received 1 February 2010

DOI:https://doi.org/10.1103/PhysRevB.82.174304