Heat pulse depolarization and short-time pyroelectricity of PVDF and copolymer

The semi-crystalline polymer PVDF and the copolymer P(VDF-TrFE) show piezo- and pyroelectric properties after poling in high electric fields. During the poling process charges are injected from the electrodes into the film. These charges are caught in coulomb traps at the surfaces of the poled crystallites causing a mutual stabilization of charges and dipoles. This is the reason for the remanence of the polarization after switching off the electric field. The binding energy of the charges is equal to the activation energy of the depolarization which means that setting free of charges from the traps is equivalent to the destruction of polarization. To learn something about the temporal behaviour in a shorter time scale than TSD measurements we use short heat pulses with rise times of some ms with a fast temperature increase of 5-30 K for partial depolarizing the samples