Impact of crystallization on ferro-, piezo- and pyro-electric characteristics in thin film P(VDF–TrFE)

Abstract

In this paper, the impact of the crystallization and polymer chain length of the P(VDF–TrFe) on its dielectric, ferroelectric, piezoelectric and pyroelectric properties are studied. X-rays diffraction (XRD) analysis have revealed that a higher β crystalline phase is obtained with a lower polymer chain length corresponding to a higher grain size for a P(VDF–TrFe) composition of 72.2/27.8mol.%. The polymer chain morphology was characterized by scanning electron microscopy (SEM) where the fibrils orientation and width were extracted. By coupling both XRD analysis and chain morphology analysis, we have established that an increase of the grain size of the polymer chain enhances the ferroelectric and piezoelectric effects of the P(VDF–TrFe) layer. On the other hand, we observed a slight degradation of its pyroelectric properties. In addition, the piezoelectric coefficient (d33) of the P(VDF–TrFe) was enhanced by decreasing the molecular weight (Mw) of the copolymer, exhibiting a maximum value around −50pC/N for the composition 72.2/27.8 with a molecular weight of 470kg/mol. On the opposite, the pyroelectric properties were enhanced for the lowest polymer crystalline grain size studied and obtained with the composition 71/29mol.% with a molecular weight of 505kg/mol. A pyroelectric coefficient of 37.8μC/m2K was measured.