Ionic conductivity, phase composition, and local defect structure of ZrO2-Gd2O3system solid solution crystals

Abstract

The crystalline structure, ionic conductivity, and local structure of ZrO2-Gd2O3solid solution crystals have been studied for a wide range of compositions. The (ZrO2)1-х(Gd2O3)хcrystals (x = 0.03–0.33) have been grown by directional melt crystallization in cold crucible. The phase composition of the crystals has been studied using X-ray diffraction and transmission electron microscopy. The transport parameters have been studied using impedance spectroscopy in the 400–900 °С range. The local structure of the crystals has been studied by optical spectroscopy with Eu3+ ion probe. The maximum conductivity at 900 °С (0.047 S/cm) has been observed in the crystals containing 10 mol% Gd2O3. This composition is close to the cubic/tetragonal phase boundary. The compositions corresponding to the single-phase cubic region exhibit a decrease in the ionic conductivities with an increase in the Gd2O3 concentration. Studies of the local structure of the ZrO2-Gd2O3 system solid solutions have revealed specific features of the formation of optical centers which characterize the localization of oxygen vacancies in the lattice depending on the concentration of the stabilizing oxide. Comparison of the experimental values of the lattice parameter with those calculated using various models has shown that the best fit between these data is provided by the model of inequiprobable distribution of oxygen vacancies. We have discussed the correlation between the crystalline and local structures and the transport parameters of the crystals. Analysis of the results allows us to identify the Gd2O3 concentration ranges in which the ionic conductivity of the crystals is mainly determined either by the phase composition or by the regularity of oxygen vacancy localization in the crystal lattice.