Charging and switching of ferroelectrets. How much can ferroelectrets behave like ferroelectrics?

Nonpolar porous electrets which are polarized due to internally charged surfaces are called ferroelectrets because of many similarities to ferroelectrics. Ferroelectrets are piezo- and pyroelectric, their polarization can he switched by means of an external field and hysteretic effects can be observed. In many respects however, ferroelectrets are different to conventional ferroelectrics. We report about the very different charging and switching mechanism in ferroelectrets, both in a simple model-system and in a cellular polypropylene foam. These mechanisms are crucial and form the basis for the striking phenomenological similarities to ferroelectrics. We report also about specific peculiarities and pitfalls related to present ferroelectrets and their characterization. High electric field strength and anelastic non-linearities can be the cause for false ferroelectric-like hysteresis-loops which do not reflect any polarization switching.