X-ray diffraction showed that the volume fraction of 90 degrees domains in tetragonal Pb(Zr,Ti)O-3 thin films could be substantially reduced by either hot de poling or by a bipolar pulsed-field process. In both cases, the (001) Bragg peak increased and the (100) peak decreased. However, ferroelectric hysteresis loops look quite different. Hot de poling leads to large internal herds and high frozen-in polarisation, whereas pulse treatment removes the Voltage shifts. This relaxation of the loop and x-ray diffraction results indicate a liberation of defect-pinned domain walls by removing, reorienting, or randomizing charged defects or defect dipoles. Alignment of defects during hot de poling contributes to piezoelectric and pyroelectric activities. (C) 1998 American Institute of Physics.