Electrode overvoltage model for a flash state of yttria-stabilized zirconia: validity, limitation, and open new issue

Since the discovery of various blackening behaviors of yttria-stabilized zirconia (YSZ) between direct current (DC) and alternating current (AC) flash treatment, several efforts have been made to explain these phenomena. In this study, we developed a novel model based on electrode overvoltage to explain the blackening behavior of YSZ. It was found that the difference in the blackening behavior by the DC and AC flash treatment of YSZ could be qualitatively explained on the basis of an electrode overvoltage model. However, the true AC-flash state is difficult to understand owing to the limit of the principal in the model. In addition, high-amplitude voltage impedance spectroscopy revealed the nonlinearity problem between the amplitude voltage and current. As a result, new methodologies and theories that are different from conventional ones are essential to clarify the true nature of the flash state of YSZ.