Ionic conductivity of ${\mathrm{ZrO}}_2$–12 mol % ${\mathrm{Y}}_2$${\mathrm{O}}_3$ single crystals

Fast ionic conductors are important to study because of their use in the construction of technologically useful devices such as electrochemical cells, oxygen monitors, and the high-temperature fuel cell. Oxygen-ion conductors form a major subgroup of these materials, and, in particular, stabilized zirconia is one of the more important solid electrolytes. However, the ionic conductivity of this material is still only rather poorly understood. The aim of the present work is to describe, by means of a method of local fits (LF’s) to Arrhenius’s law, the experimental values of the ionic conductivity of ${\mathrm{ZrO}}_2$–12 mol % ${\mathrm{Y}}_2$ ${\mathrm{O}}_3$ single crystals in the temperature range from 200 °C to 1600 °C. This method yields two sets of data: the preexponential factor, ${\mathit{A}}_{\mathrm{LF}\mathit{i}}$, and the activation enthalpy, Δ${\mathit{H}}_{\mathrm{LF}\mathit{i}}$. The ln${\mathit{A}}_{\mathrm{LF}\mathit{i}}$ versus ΔS(T)/k plot [where ΔS(T) is the entropy change in the process] is a very good test of the accuracy of the LF method. The Δ${\mathit{H}}_{\mathrm{LF}\mathit{i}}$ values are fitted by a least-squares procedure to an empirical temperature-dependence function with four adjustable parameters. In order to interpret these results and to understand the physical meaning of the fitted parameters, a microscopic model is proposed that allows us to deduce a theoretical function of temperature for the activation enthalpy similar to the empirical function.