Study of the nearly constant dielectric loss regime in ionic conductors with pyrochlore-like structure

We report on ac conductivity measurement of oxide ion conductors with composition Gd2(ZryTi1-y)2O7 and a pyrochlore type structure, at temperatures between -20 and 250 degree centigrade and in the frequency range from 1 Hz to 3 MHz by using impedance spectroscopy. Results show that a crossover from a power law dependence 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 ENCL to be much lower than the activation energy Edc for the dc conductivity. We also found that the values of ENCL are almost independent of composition, and therefore of the concentration of mobile oxygen vacancies, unlike those of Edc. Moreover, for each composition, the values of ENCL=0.67±0.04 eV are very similar to those estimated for the energy barrier for the ions to leave their cages, Eα=0.69±0.05 eV. These results support that the nearly constant loss behavior, ubiquitous in ionic conductors, is originated from caged ion dynamics. (Author) 33 refs.