Non-stoichiometry and point defect structure of monoclinic and tetragonal zirconia (ZrO2+δ)

A thermogravimetric study has been performed on the nonstoichiometry of very pure monoclinic and tetragonal zirconia, ZrO2+δ, as a function of oxygen activity at temperatures between 900 and 1400 C. In the temperature range investigated, the deviation of stoichiometry, δ, as a function of oxygen activity is described in good approximation. These observed oxygen activity dependencies suggest that at least two types of point defects are present as majority defects in both monoclinic and tetragonal zirconia. Based on the non-stoichiometry data, it is proposed that the majority defects in both monoclinic and tetragonal zirconia are completely ionized zirconium vacancies at high oxygen activities and doubly charged oxygen vacancies at low oxygen activities, which are charge compensated by holes and electrons, respectively