ABSTRACT
Recent investigations indicate that oxygen ion vacancies play an important role in the phase stability, phase transformation, and properties of zirconia polycrystals. The effective double positive charged oxygen vacancies are considered as quasi-chemical species which contribute in the same manner to the stability of zirconia as low-valent cations. The oxygen vacancy concentration is primarily responsible for the metastability of the t- and c-ZrO2 phases at room temperature. Variation of the oxygen vacancy concentration in the oxygen sublattice of zirconia can be used to control the stabilization of any single phase at room temperature. Decreasing the oxygen vacancy concentration leads, for example, to a breakdown of the c-phase which transforms to the t- or m-phase. The oxygen vacancies appear to be closely involved with the grain growth. The results indicate that the single zirconia phases are stabilized in part by a crystal-chemical mechanism and in part by a physical mechanism. Phase stability mechanisms and the correlation between oxygen vacancies, phase stability, phase transformation, and properties will be discussed.
