Thermodynamic correlation among defects in ceria-zirconia solid solutions

The oxide ionic, electron and hole conductivides as well as the surface reaction rate in yuria stabilized zirconia, yttria doped ceria and their solid solutions (Zr1-xCex)Y0.2O1.9 (x = 0.0 - 1.0) are discussed in terms of the thermodynamic properties and the observed physicochemical properties. Focus is placed on a comparison between the macroscopic thermodynamic description and the microscopic defect chemical description. The microscopic thermodynamic properties have been derived from the phase diagram information together with emf and other thermodynamic properties. The microscopic properties are based on the ionic configuration of oxide vacancies reported in the literature. From the macroscopic properties, the electron and the hole conductivities have been correlated with the chemical potential and its related concentration of cerium trivalent ions and the concentration of the hypothetical species, YOO, which is determined from the chemical potential of YO1.5. The proton solubility has been correlated with the chemical potential of YO1.5 in a similar manner as the hole conductivity, that is, chemical species, YOOH, was used to represent the protons in solid solutions. The chemical potential of YO1.5 is discussed in terms of the ionic configuration, that is, the oxide ion vacancy formation in the location of the nearest neighbor or the next nearest neighbor. This makes it possible to correlate the proton solubility and the hole conductivity from the microscopic point of view. The change in the ionic configuration of the oxide ion vacancies explains the decrease in the ionic conductivity in the middle of the concentration range. On the other hand, the maximum value in the surface reaction rate for the oxygen isotope exchange reaction in the middle can be ascribed partly to the electron behavior even in the oxidative atmosphere.