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