The defect structure of the double layer in yttria-stabilised zirconia

The space charge density of 2–10 mol% yttria-stabilised zirconia (YSZ) at the interface with a gold electrode was determined from differential capacity measurements at 748–848 K. The oxygen vacancy fraction in the space charge layer was calculated as function of bias potential, temperature and composition by fitting the data at positive bias potential to a Boltzmann-type equation. The vacancy concentration in the space charge layer increases with decreasing bias potential and reaches a temperature-dependent maximum. This behaviour can be understood under the assumption that only a fraction of the oxygen sub-lattice is available for oxygen vacancy distribution. This volume fraction increases with temperature, with an associated thermal activation energy in the range of 0.27 to 0.46 eV, depending on composition.