ACTIVATION ENTROPY AND GIBBS FREE-ENERGY FOR CONDUCTION IN YTTRIA-STABILIZED-ZIRCONIA SINGLE-CRYSTALS

The temperature dependence of the activation Gibbs free energy [Delta G(T)] and entropy [Delta s(T)] associated with electric conduction in 12 mol% yttria-stabilized-zirconia single crystals was analyzed. In or der to determine the Delta G(T) and Delta S(T) functions exactly, it w as necessary to impose temperature-behavior conditions on the activati on Gibbs free energy to give Delta S(T --> infinity) = 0. The temperat ure dependence of the entropy was similar to that of the activation en thalpy. Both reach stable values at low temperatures (extrinsic associ ated range). In this temperature range, Delta G(T) shows a linear beha vior. At higher temperatures, Delta G(T) decreases asymptotically to a value approximately equal to the migration enthalpy of the oxygen vac ancies. A value of 5.6x10(-7) eV/K was calculated for the variation of entropy associated with the migration of the vacancies. Assuming the cation-vacancy-cation association to be a first-neighbor structure, a value of 4.85x10(-4) eV/K was found for the association entropy of the vacancies. These results are in very good agreement with those obtain ed by applying the method used in alkaline halide studies.