We investigate the nature of atomic relaxations around oxygen-vacancy defects in the ferroelectric perovskite ${\mathrm{PbTiO}}_3$ 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.

• Received 22 September 1997

DOI:https://doi.org/10.1103/PhysRevB.57.R13961