Distribution of the Ferroelectric Polarization in Polyvinylidene Fluoride During Initial Poling and Polarization Reversal

The polarization profiles dynamics in polyvinylidene fluoride (PVDF) films was studied in situ by the piezoelectrically induced pressure step method. It was shown that a substantially inhomogeneous polarization profile was formed during poling and reversal switching in medium fields with the maximum of polarization near the positive electrode. However, poling of virgin samples in strong fields resulted in formation of a homogeneous polarization profile that remained uniform and easily switchable at any subsequently applied field. It appeared that it was impossible to improve the polarization homogeneity in PVDF by application of strong fields, if original poling was performed in weak or medium fields. The observed features were explained by a model assuming injection of negative charges and formation of a permanent blocking layer at the boundary between polarized and non-polarized zones. The obtained results should be considered while selecting poling conditions in design and production of sensors and actuators based on PVDF. The results have a practical importance in design of piezo- and pyro- sensors and activators using the ferroelectric PVDF films, because they should be considered while selecting poling conditions.