Electrical properties of ZrO2–Gd2O3 ceramics

ZrO2 doped with aliovalent oxides, such as CaO, Y2O3 and Gd2O3 etc., is a good structural material as well as an ionic conductor. In the present work, the impedance spectroscopic studies of Gd2O3 doped ZrO2 ceramics (Gd2O3 between 1.75 and 11 mol.%) are carried out in the temperature range from 200 to 425 °C. The 4 and 2.5 mol.% Gd2O3–ZrO2 samples show highest grain and grain boundary conductivity. The grain and the grain boundary conductivities attain very high values in the single phase (tetragonal or cubic) regions and have low values at compositions where a mixture of phases exist. This is more pronounced for the grain boundary conductivity. Activation enthalpies for conduction in ZrO2–Gd2O3 ceramics, obtained from the Cole–Cole plot, are similar to those for the Y2O3–ZrO2. The activation enthalpies for ZrO2–Gd2O3 ceramics are lower in the samples containing monoclinic phase and in the cubic phase region (>8 mol.% Gd2O3). Activation enthalpy for conduction based on the relaxation frequency obtained from the modulus spectra agree with those obtained using the Cole–Cole plots. The Almond–West AC conductivity model has been used to evaluate the Jonscherʹs constant and the hopping frequency. Migration enthalpy is calculated by curve fitting to this model. Unlike Y2O3–ZrO2, the Gd2O3–ZrO2 ceramics show no activation enthalpy for association, indicating that there is no association between vacancies to form clusters.