Complex-impedance analysis for the development of zirconia oxygen sensors

Abstract

The complex impedance of Pt, Au and Ag electrodes in contact with a solid electrolyte, yttria-stabilized zirconia, was examined in the range 300–1000°C. The real and imaginary components were measured over the frequency range from dc to 100 kHz in three ways. The complex-impedance plot was characterized by two semi-circles. Considering the correlation between different thicknesses of the solid electrolyte, the semicircle in the high-frequency range was found to be due to oxygen ion relaxation due to the impurity phase formed in the electrolyte. On the other hand, the semicircle in the low-frequency range showed a characteristic distortion to an arc depending largely on the process by which the electrode was prepared and also on the electrode material. The impedance-plane plot for different equivalent circuits was calculated with various parameters. A reasonable equivalent circuit for the arc was obtained, and the analysis has been proved to be very useful for the development of oxygen sensors.