Influence of phase composition and local crystal structure on the transport properties of ZrO2−Y2O3 and ZrO2−Gd2O3 solid solutions

Abstract

The results of investigation of crystal structure, ion conductivity and local structure of solid solutions (ZrO2)1−x(Gd2O3)x and (ZrO2)1−x(Y2O3)x (x = 0.04, 0.08, 0.10, 0.12, 0.14). The crystals were grown by directional crystallization of the melt in a cold container. The phase composition of the crystals was studied by X−ray diffractometry and transmission electron microscopy. Transport characteristics were studied by impedance spectroscopy in the temperature range 400—900 °C. The local crystal structure was studied by optical spectroscopy. Eu3+ ions were used as a spectroscopic probe. The results of the study of the local structure of solid solutions of ZrO2—Y2O3 and ZrO2—Gd2O3 systems revealed the peculiarities of the formation of optical centers, which reflect the nature of the localization of oxygen vacancies in the crystal lattice depending on the stabilizing oxide concentration. It is established that the local crystal environment of Eu3+ Ions in solid solutions (ZrO2)1−x(Y2O3)x and (ZrO2)1−x(Gd2O3)x is determined by the stabilizing oxide concentration and practically does not depend on the type of stabilizing oxide (Y2O3 or Gd2O3). The maximum conductivity at 900 °C was observed in crystals containing 10 mol.% Gd2O3 and 8 mol.% Y2O3. These compositions correspond to the t′′−phase and are close to the boundary between the regions of the cubic and tetragonal phases. It was found that in the system ZrO2—Y2O3 stabilization of the highly symmetric phase occurs at a lower stabilizing oxide concentration than in the system ZrO2—Gd2O3. Analysis of the data obtained allows us to conclude that in this range of compositions the main influence on the concentration dependence of the ion conductivity has a phase composition, rather than the nature of the localization of oxygen vacancies in the crystal lattice.