Conductivity induced polarization in two-phase ferroelectric materials

It is commonly believed that formation of polarization and its switching in ferroelectrics is a fast phenomenon. In the present study it was found, however, that in semicrystalline ferroelectric polymers, containing both crystalline and amorphous phases, polarization continues to grow under an applied field during times 5-6 orders of magnitude longer than the reported switching times. It is demonstrated that the controversy can be resolved by taking into account the effect of conductivity in such materials. It is shown that there are two temporal contributions to the ferroelectric polarization, of which the first one is field dependent and originates from a fast alignment of dipoles in crystallites, while the second slow component is controlled by conductivity. Appropriate modeling reveals the importance of charge accumulated at the interfacial boundaries to form the slow ferroelectric polarization contribution. Good agreement of calculated and measured polarization has been observed for PVDF.