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.