Oxygen vacancies contributing to intragranular electrical conduction of yttria-stabilized zirconia (YSZ) ceramics

The behaviors of oxygen vacancies, which dominate electrical conduction within the grains of Zr0.85Y0.15O2 - (delta) (non-doped YSZ) ceramics, were investigated by dielectric measurements as a function of temperature. Trials were carried out to identify the trapping center for oxygen vacancies at low temperatures by partially substituting Hf4+ or Sc3+ for Zr4+ or Y3+ (doped YSZ). The bulk resistance obtained by impedance analysis and the relaxation process of the dielectric loss tangent yield estimates of the migration energy of O2- ion, EM, and the dissociation energy required to extricate an oxygen vacancy from the trapped state, EO. The dielectric results for doped YSZ suggest that the excess oxygen vacancies are preferentially bound to Zr4+ rather than Y3+ in non-doped YSZ. In Zr0.85Y0.15O2 - (delta), intragranular electrical conduction results from O2- migrations with EM = 1.01 (plus-minus) 0.02 eV, which require the assistance of free mobile oxygen vacancies that are thermally dissociated from their bound state by Zr4+ with EO = 50 (plus-minus) 1 meV.