Semicrystalline materials like polyvinylidene fluor-ide (PVDF) and its copolymers with either tri-fluoroethylene (P(VDF-TrFE)) or tetrafluoroethylene (P(VDF-TFE)) possess spontaneous switchable po-larization in crystalline phase and form a new class of dielectrics called ferroelectric polymers [1,2]. It has been shown recently that high stability of the remnant polarization in PVDF and P(VDF-TrFE) results from its interaction with injected charge trapped at the boundaries of either crystallites or macroscopic polarized zones [3-6]. In both cases, polarization and space charge form a stable and self-consistent system, with the latter playing a decisive role. Assuming Debye's approximation for relaxation and continuous distribution of activation energies for charge detrapping, we obtained this distribution for PVDF and P(VDF-TrTE) [3]. The purpose of this work was to find how the space charge affects thermal stability of residual polarization in P(VDF-TFE) copoiymer, which also belongs to a class of ferroelectric polymers [7, 8], but is much less studied than PVDF and P(VDF-TrFE). To accomplish this we measured profiles of polarization in poled P(VDF-TFE) samples as a function of temperature during linear heating from 20 °C to the melting point of crystallites. The activation energy was calculated by fitting experimental data to a recently proposed theoretical model [3] and the obtained results were compared with those known for PVDF and P(VDF-TrFE) copoiymer.
展开▼
