A. Yu. Belov

Creep in Soft PZT: The Effect of Internal Fields

The effect of internal fields on the activation energy of creep in polycrystalline ferroelectric ceramics is investigated. It is shown that the internal fields can be evaluated directly from the experimental curves for polarization creep under constant electric field. For this purpose a micro-mechanical model of thermally activated ferroelectric switching is modified by taking into account the dependence of the activation energy on the internal fields within the framework of a phenomenological mean-field approximation. The modified model has the form of an Arrhenius type equation containing the structural parameters like the spontaneous polarization only via the effective fields acting on the domain walls. As an example, a rationalization of the experimental room-temperature creep curves in a soft lead zirconate titanate piezoceramic PZT-5H on the basis of the model is carried out. It is shown that the main part of the internal field, which is linear in the spontaneous polarization and responsible for the logarithmic creep, can be directly extracted from such data sets.

Micromechanics of Ferroelectrics: From Domain Walls to Piezoceramic Devices

A micromechanical approach utilizing the features of thermally activated domain wall motion is applied to simulate the structural changes in ferroelectric ceramics for the basic processes employed in piezoelectric devices. The approach combines an Arrhenius equation (with the temperature insensitive pre-exponential factor) for the domain wall mobility and a time-dependent constitutive model, using the volume fractions of domains with representative polarization directions as structural (internal) variables. Computer simulation of the piezoceramic poling process in a sheet actuator with interdigitated electrodes shows the formation of the inhomogeneous poling state and peculiarities of the nonlinear longitudinal piezoelectric effect. **Permanent address: Institute of Crystallography RAS, Moscow, Russia.

The Evaluation of Activation Parameters for Ferroelectric Switching in Soft PZT Ceramics

The dependence of the coercive field and remanent polarization on temperature was measured for a number of commercial soft PZT ceramics in the temperature range from −175°C to 150°C. It is found that for all ceramics investigated the curves E c vs. T have a peak in the low temperature region, typically between −100°C and −50°C. As temperature increases in the range from 0°C to 150°C the coercive field decreases nearly linearly. The temperature dependence of the coercive field in this region is explained by means of a micromechanical model based on an Arrhenius equation for the mobilility of domain walls and is used to calculate the activation energy for the domain wall movement in the field of short-range obstacles. Possible effects of microstructure on the activation energy are discussed.