Low field depoling phenomena in soft lead zirconate titanate ferroelectrics

Reduction in polarisation of ferroelectric materials due to repeated electrical cycling is a major problem in ferroelectric non-volatile memory devices. There is a large amount of data addressing this issue at high electric field strengths under bipolar loading conditions, however the effect of field cycling at low electric field strengths (< E_c) has not been fully investigated. This paper addresses the effects of repeated cycling of soft lead zirconate titanate using electrical pulses at fields well below the coercive field strength of the material. It is shown that this mode of loading diminishes the macroscopic polarisation and mechanical response of the material. The origins of this behaviour are found to be a statistical non-non-reversible switching processes that does not result in classical fatigue related mechanical microstructural damage or defect agglomeration and domain pinning. Instead the process is fully recoverable and attributed to local changes in switching energy and clustering of switched ferroelectric cells.