High ionic conductivity in the pyrochlore-type Gd2 − yLayZr2O7 solid solution (0 ≤ y ≤ 1)

As SOFC technology relies at present on La-based perovskites as cathode materials, we have analyzed the effect La-incorporation might have in the ionic conductivity of P-Gd2Zr2O7, a pyrochlore-type fast oxygen ion conductor. Single phase powder samples with different La/Gd ratio, were prepared in the pyrochlore-type Gd2 − yLayZr2O7 solid solution (0 ≤ y ≤ 1) by mechanically milling stoichiometric mixtures of the corresponding oxides. Electrical conductivity measurements were performed for different compositions by using pressed pellets sintered at 1500 °C, as a function of frequency and temperature. Despite of increasing structural ordering (decreasing number of mobile charge carriers), it was found that oxide–ion conduction at intermediate temperatures is almost La-content independent for y ≤ 0.8 because of decreasing dc activation energy (from 1.13 to 0.85 eV). We show that these results can be explained in terms of weaker ion–ion interactions in better ordered structures (i.e., rich La-content), highlighting the importance of structural ordering/disordering in determining the dynamics of mobile oxygen ions.