Space Charge and Dipolar Contributions from Amorphous and Crystalline Phases in Ferroelectric Polymers

Abstract

Piezoelectric and pyroelectric properties in semicrystalline polymers originate from dipole disorientation, dimensional changes in the amorphous and crystalline phases, motion of charges necessary for compensation and stabilizing the polarization of the crystallites and reversible changes of crystallinity. Using thermally stimulated discharge currents, isothermal charging and discharging currents the relaxation of space charge and dipolar charge are analyzed. The measurements were carried out for polyamide 11 in a large temperature range below and above the glass-rubber transition temperature of the amorphous phase and for different fields and times to allow an effective selective polarization. By appropriate choice of the polarization parameters, the effects related with permanent dipoles in the crystalline phase, the polarization of the dipoles in the amorphous phase, the effect of the space charge and interfacial polarization are identified. The major part of the charge measured during charging is stored in the sample. The polarization induced by stretching of the sample at room temperature is very stable up to temperatures as high as 150°C.