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Universal scaling features of polarization switching are established experimentally in rather different classes of disordered ferroelectrics: in well-studied lead-zirconate titanate (PZT) ferroelectrics, in recently synthesized Custabilized 0.94(Bi 1/2 Na 1/2 )TiO 3 -0.06BaTiO 3 (BNT-BT) relaxor ferroelectrics, and in classical organic ferroelectrics P(VDF-TrFE). These scaling properties are explained by an extended concept of an inhomogeneous fi eld mechanism (IFM) of polarization dynamics in ferroelectrics. Accordingly, disordered ferroelectrics exhibit a wide spectrum of characteristic switching times due to a statistical distribution of values of the local electric fi eld. How this distribution can be extracted from polarization measurements is demonstrated. Generally, it is shown that the polarization response is primarily controlled by the statistical characteristics of disorder rather than by a temporal law of the local polarization switching.

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.

Sandwiched structures of open-porous and solid polymer dielectrics reveal a strong piezoelectric response after proper charging by high electric fields. Here, the electrical properties of corona-poled three-layer FEP/ePTFE/FEP sandwiches are studied theoretically and experimentally with the objective of its possible optimization for the highest piezoelectric activity. Modelling of the charging properties is performed for different sandwich geometries. It is shown that the maximum value of the remanent interface charge density accumulated during poling depends mainly on the ratio of the solid and porous layers thicknesses and on parameter E B, which characterizes the electric breakdown strength of air in the porous layer. E B exhibits specific dependences on porosity and thickness of the porous layer. For a given porous layer E B is independent of the solid film thickness. The obtained results can be utilized to further optimize the sandwich structure as an electromechanically active device.

The influence of Pt, tin-doped In 2 O 3 , and RuO 2 electrodes on the electrical fatigue of bulk ceramic Pb͑Zr, Ti͒O 3 ͑PZT͒ 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.

The dynamics of polarization switching in a soft lead-zirconate-titanate ceramic has been studied over a broad time window ranging from 10−6–106 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.

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Analysis of polarization switching dynamics by means of the inhomogeneous field mechanism model allows insight into the microscopic mechanism of reversed polarization domain nucleation. For all chemical compositions studied, two distinct field regions of nucleation are established. In the high-field region, the activation energy barrier is found to be inversely proportional to the local field according to the Merz law. In contrast, the barriers in the low-field region exhibit a linear field dependence with a minimum in the compositional region of phase instability, which can explain the corresponding peak ferroelectric properties.