Blocking Effect of ZnO in YSZ/ZnO Composites

Abstract

Impedance spectroscopy analysis was performed under different oxygen pressures, on dense YSZ/ZnO composites with a ZnO content varying from 3 to 25 vol% and two concentrations, 8 and 10 mol% of Y2O3 in YSZ. Raman spectroscopy showed that the cubic zirconia phase containing 8 mol% Y2O3 is not stable in contact with ZnO, under the selected sintering conditions (1300°C, 2 h), in contrast to that containing 10%. The impedance diagrams reveal a peculiar blocking effect associated with the ZnO grains. Its magnitude is quasi independent of the large variations of the ZnO conductivity, associated with changes in the equilibrium oxygen pressure. On the other hand, its relaxation frequency markedly depends on the non-stoichiometry of this compound. These peculiar properties are interpreted in terms of a pseudo-capacitive behavior of the electronically conducting ZnO in contact with the YSZ ionic conductor. This contact forms an electrode, the potential of which being determined by the non-stoichiometry of ZnO.