Temporal behavior of ferroelectric ceramics during the polarization switching cannot be satisfactorily explained by simple Debye or even stretched exponential laws. These materials exhibit rather a wide spectrum of characteristic times interpreted by different authors as switching or nucleation waiting times, the physical reasons for a wide time distribution still remaining unclear. A new model of polarization switching presented here suggests that the characteristic time variance in the ferroelectrics originates from the random distribution of the local electric fields due to intrinsic randomness of the material. The presented theory allows a direct extraction of the distribution of field values from the experiment. Systematic studies of polarization switching in fatigued lead zirconate titanate demonstrate the evolution of the field distribution with increasing level of fatigue. Plausible cause of the formation of regions subject to different field strengths is the generation of defects such as microcracks, pores, or voids in the course of fatigue. Suitability of the proposed model is demonstrated by an excellent correlation between experimental and calculated data for virgin and differently fatigued samples in a broad time-field region covering the electric field values of 0.5\char21{}2.5 kV/mm and nine orders of the magnitude of poling time.

The dynamics of polarization switching in a soft lead-zirconate-titanate ceramic has been studied over a broad time window ranging from ${10}^{-6}–{10}^6$ for applied fields between 0.5 and 2.5 kV/mm. The classical Kolmogorov–Avrami–Ishibashi model of the polarization reversal was not able to satisfactory explain the obtained results. Therefore, a new concept for the polarization dynamics of ferroelectric ceramics has been suggested, which is based on two principal assumptions, (1) a strong dependence of the polarization switching time on the local electric field and (2) a random distribution of the local switching times caused by an intrinsic randomness in the field distribution within the system. Thereby the switching volume is composed as an ensemble of many regions with independent dynamics governed by local field exclusively. Such random field distribution could be well adjusted by a Gaussian distribution around the mean value of the field applied. A total polarization dependence on time and applied field was obtained in explicit form with only three fitting parameters which enabled a good description of the experimental results on polarization reversal in the whole time-field domain.

Polymers with electrically charged internal air cavities (ferroelectrets) reveal a pronounced piezoelectric response and are regarded as soft electroactive multi-functional materials. This work presents preliminary results on the preparation and piezoelectric effect of ferroelectrets based on the polylactic acid (PLA) polymer. A distinctive feature of the manufactured films is that they are biodegradable. After a microstructure modification of carbon dioxide (CO₂) foamed PLA sheets by hot-pressing treatment and corona polarization, these cellular films reveal large piezoelectric $d_{33}$ and $d_{31}$ responses in both quasi-static and dynamic modes. For freshly charged films, the maximum quasi-static piezoelectric coefficients are about 600 pC/N ($d_{33}$ ) and 44 pC/N ($d_{31}$ ) for a relatively thick film of 360 μm and a nominal porosity of about 60%. During the first 20 days after polarization, the piezoelectric activity decreases by half compared to the primary value, but then remains almost unchanged for a long time. Due to an already established inherent biocompatibility of PLA polymers, these eco-friendly ferroelectrets can be potentially used in various biological applications such as biosensors and microenergy harvesters embedded in tissue and artificial muscles.

Open-porous polymers form an attractive class of piezoelectric materials. Up to now it has been demonstrated that fibrous polyterafluoroethylene films after proper polarizing are responsible for the high piezoelectric response if confined between two electrically blocking polyfluoroethylene propylene layers. The sandwich structures reveal large quasistatic piezoelectric coefficients of up to 1500 pC/N. Here a theoretical model is proposed for a three-layer sandwich which quantitatively explains the experimentally obtainable polarization and its hysteresis behavior for different poling voltages. It will be reported that each sandwich structure exhibits a limit for the remanent polarization induced by polarization backswitching due to insufficient charge compensation. The correlation of the remanent polarization to the device geometry and the dielectric constants will be highlighted and suggestions for optimization will be given. It will be reported that the limitation of the remanent polarization also limits the obtainable piezoelectric coefficient of the sandwich structures.

The influence of Pt, tin-doped ${\text{In}}_2{\text{O}}_3$ , and ${\text{RuO}}_2$ electrodes on the electrical fatigue of bulk ceramic $\text{Pb}\left(\text{Zr},\text{Ti}\right){\text{O}}_3$ (PZT) has been studied. Schottky barrier heights at the ferroelectric/electrode interfaces vary by more than one electronvolt for different electrode materials and do not depend on crystallographic orientation of the interface. Despite different barrier heights, hysteresis loops of polarization, strain, permittivity, and piezoelectric constant and the switching kinetics are identical for all electrodes. A 20% reduction in polarization after ${10}^6$ bipolar cycles is observed for all the samples. In contrast to PZT thin films, the loss of remanent polarization with bipolar switching cycles does not significantly depend on the electrode material.