  The formation and field-induced switching of defect dipoles in acceptor doped
lead titanate is described by a kinetic model representing an extension of the
well established Arlt-Neumann model [Ferroelectrics {\bf 76}, 303 (1987)].
Energy barriers for defect association and reorientation of oxygen
vacancy-dopant (Cu and Fe) complexes are obtained from first-principles
calculations and serve as input data for the kinetic coefficients in the rate
equation model. The numerical solution of the model describes the time
evolution of the oxygen vacancy distribution at different temperatures and
dopant concentrations in the presence or absence of an alternating external
field. We predict the characteristic time scale for the alignment of all defect
dipoles with the spontanenous polarization of the surrounding matrix. In this
state the defect dipoles act as obstacles for domain wall motion and contribute
to the experimentally observed aging. Under cycling conditions the fully
aligned configuration is perturbed and a dynamic equilibrium is established
with defect dipoles in parallel and anti-parallel orientation relative to the
spontaneous polarization. This process can be related to the deaging behavior
of piezoelectric ceramics.
