Microscopic study of oxygen-vacancy defects in ferroelectric perovskites

We investigate the nature of atomic relaxations around oxygen-vacancy defects in the ferroelectric perovskite PbTiO3 through first-principles pseudopotential total energy calculations. A tail-to-tail polarization is one of the patterns, that emerges from atomic relaxations around oxygen vacancies and its stability is found to be enhanced by charge trapping. Oxygen vacancies in Ti-O-Ti chains along the polarization axis are more favorable than those in Ti-O-Ti planes normal to the axis. The possible role of oxygen vacancies in fatigue and aging is discussed.