Pyrochlore to perovskite phase transformation in sol-gel derived lead-zirconate-titanate (PZT) films was studied by x-ray diffraction and transmission-electron microscopy (TEM). X-ray diffraction studies of PZT films on sapphire substrates indicated that the pyrochlore to perovskite phase transformation was completed at 650-degrees-C. In contrast, TEM investigations of free-standing PZT films showed that the phase transformation was completed at much higher temperatures. This discrepancy in the behavior of free-standing films versus films on substrate can be related to the size effect.