Abstract
Impedance spectroscopy was performed on dense YSZ/ZnO composites with a ZnO content varying from 3 to 25 vol% and under different oxygen pressures. Raman spectroscopy showed that the cubic zirconia phase is not fully stable in contact with ZnO, under the selected sintering conditions (1300°C, 2h). The impedance diagrams reveal a peculiar blocking effect associated with the ZnO grains. Its magnitude is independent of the large variations in conductivity of ZnO, associated with changes in the equilibrium oxygen pressure. Its relaxation frequency markedly depends on this parameter. 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 predominant point defect concentration in ZnO.
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