  Point defect migration is considered as a mechanism for aging in
ferroelectrics. Numerical results are given for the coupled problems of point
defect migration and electrostatic energy relaxation in a 2D domain
configuration. The peak values of the clamping pressure at domain walls are in
the range of $10^6$ Pa, which corresponds to macroscopically observed coercive
stresses in perovskite ferroelectrics. The effect is compared to mechanisms
involving orientational reordering of defect dipoles in the bulk of domains.
Domain clamping is significantly stronger in the drift mechanism than in the
orientational picture for the same material parameters.
