Effect of Aging on Yttria‐Stabilized Zirconia: I. A Study of Its Electrochemical Properties

The causes of the decrease in electrical conductivity with aging in ‐stabilized zirconia, an oxygen‐ion conductor, were studied. This study was carried out using the dc four‐probe technique for measuring electrical conductivity and the activation energy for the migration of oxygen ions. The results show that conductivity decreased with aging below certain temperatures in all specimens. Moreover, it was found that conductivity decreases significantly as the temperature decreases. Samples that were aged at relatively low temperatures exhibited a decrease in conductivity and an increase in activation energy. It was concluded that short range ordering of oxygen ion vacancies toward the zirconium to relax the anistropy of the lattice distortion is the cause of the decrease in electrical conductivity and the increase in activation energy. When aging was carried out at a relatively high temperature, fully stabilized zirconia showed no change in activation energy and only a slight increase in conductivity. This is because oxygen ion vacancies are in the disordered state and the cubic phase is the only phase at this temperature. Short range ordering of oxygen ion vacancies takes such a long time presumably because these oxygen ion vacancies are still able to move even after aging. This was explained using the concept of mean first passage time.