Electrical properties of ZrO 2–Gd 2O 3 ceramics

Abstract

ZrO 2 doped with aliovalent oxides, such as CaO, Y 2O 3 and Gd 2O 3 etc., is a good structural material as well as an ionic conductor. In the present work, the impedance spectroscopic studies of Gd 2O 3 doped ZrO 2 ceramics (Gd 2O 3 between 1.75 and 11 mol.%) are carried out in the temperature range from 200 to 425 °C. The 4 and 2.5 mol.% Gd 2O 3–ZrO 2 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 ZrO 2–Gd 2O 3 ceramics, obtained from the Cole–Cole plot, are similar to those for the Y 2O 3–ZrO 2. The activation enthalpies for ZrO 2–Gd 2O 3 ceramics are lower in the samples containing monoclinic phase and in the cubic phase region (>8 mol.% Gd 2O 3). 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 Jonscher's constant and the hopping frequency. Migration enthalpy is calculated by curve fitting to this model. Unlike Y 2O 3–ZrO 2, the Gd 2O 3–ZrO 2 ceramics show no activation enthalpy for association, indicating that there is no association between vacancies to form clusters.