Piezo- and pyroelectric hysteresis in thin unipolar PZT films

Piezo- and pyroelectric hysteresis loops have been studied in unipolar lead zirconate titanate (PZT) films grown on silicon substrates. The PZT film compositions corresponded to the region of a morphotropic phase boundary. It is established that the degree of unipolarity (spontaneous polarization) in such films can reach a level that is close to the magnitude of residual polarization. Cyclic poling of samples in a strong electric field leads to a sharp drop of the residual polarization, which is related to the pinning of domain walls and the action of external tensile mechanical stresses on the film.