90° domain wall relaxation and frequency dependence of the coercive field in the ferroelectric switching process

The mechanisms involved in the polarization switching process in soft andhard Pb(Zr53, Ti47)O3 (PZT) bulk ceramics were investigated through thedependency of the hysteresis loop on the frequency. In order to determine theinfluence of the defects on the domain switching dynamics the samples werecharacterized in the virgin state and after a fatigue or a depinning process.The frequency dependence of the polarization revealed a strong relaxation ofthe 90 domain walls at 100 Hz. The results also revealed a strong influence ofthe kind of defect and their distribution into the ferroelectric matrix on thedomain switching dynamics, which reflected in the frequency dependence of thecoercive field and the percentage of the backswitching. Initially, it wasobserved that the frequency dependence of the coercive field for the soft andthe hard PZT in the virgin state had just one rate of change per decade in allfrequency range investigated, which is the standard behavior found in theliterature. However, after the fatigue or the depinning process two rates ofchanges were noticed. Consequently, an evidence of an upper frequency limit forthe coercive field changes was found. The percentage of the backswitching andits behavior for the soft PZT was almost independent of the fatigue state inall frequency range investigated. Nevertheless, for the hard PZT an oppositebehavior was verified. The reorientation of the domains was modeled asoccurring in a viscous medium where several forces such as viscous andrestoring forces act on them