Peculiarities of the polarization build-up and its relaxation in corona poled PVDF films meant for manufacturing of pyro- and piezoelectric sensors have been revealed from the complex experimental investigation of the polymer. It has been found that the polarization and the space charge are interrelated forming a self-balanced system. Its stability depends mainly on charges trapped in the volume. It has been shown that the charge trapping occurs in macroscopic zones positioned at the borders of completely polarized parts of the volume. The trapped charges play an important role in stability of the ferroelectric polarization, since they neutralize the depolarizing field.

It is established that for obtaining the prolonged stability at elevated temperatures it is necessary to perform preliminary annealing; moreover the temperature of annealing must be somewhat higher than the assumed temperature of operation. Properties of the sensor remain constant for the duration of prolonged time. It is revealed that the maximum temperature of the operation of the developed pyroelectric and piezoelectric sensors should not exceed 80 °C. It is advisable toestablish the lower boundary of the range of operating temperatures at the level of -20…-25 °C taking into account that the glass transition temperature of the PVDF amorphous phase is in the range of -40…-50 °C.

Experimental results are presented on anomalous behavior of absorption currents in PVDF during the stepwise increase of the voltage applied through a corona. These results, supplemented with the dynamics of the time constant of the electret potential decay are consistent with a hypothesis assuming deep trapping of the charge carriers during the polarization buildup in ferroelectric polymers. Model calculations are made on distribution of the potential energy at the surface of the polarized crystallites proving that additional sites for the charge trapping are created there.

Experimental evidence is provided on close relation between polarization and space charge in corona poled PVDF films. It is shown that the depolarizing field is compensated by charges trapped in macroscopic transition zones, by which polarized parts of the volume are separated from non-polarized ones. The compensating charges are either injected in the bulk, or created inside due to the thermal emission and then trapped when the ferroelectric polarization in crystallites is formed.

Four modifications of the corona triode are described for charging polar polymers with ferroelectric or non-linear optical properties. Advantages of the constant current modification of corona poling are illustrated and discussed.

The procedure has been developed for extracting homocharge and heterocharge currents from experimentally measured thermally stimulated depolarization currents of corona poled PVDF. Application of different depolarization modes supplemented with the isothermal currents allowed to obtain such parameters of relaxation processes, as activation energies, characteristic frequencies and time constants.

Using short circuit and open circuit modifications of the thermally stimulated depolarization current technique, relaxation currents have been measured in corona poled copolymer of vinylidene fluoride with tetrafluoroethylene in samples stored after poling for either 1 day, or 16 month. Two well structured peaks observed in aged samples were attributed to relaxation of electret and ferroelectric components of the remnant polarization. In fresh samples the two components were mixed forming one broad peak. Relaxation of the space charge caused inversion of the current in the open circuit mode both in fresh and in aged samples. Space charge peaks extracted from the total current by appropriate calculations have shown that the trapped charges were more stable than the polarization. It was suggested that both the electret and the ferroelectric components of the remnant polarization were accompanied by either space, or surface charges.