Extrinsic versus intrinsic ferroelectric switching: experimental investigations using ultra-thin PVDF Langmuir-Blodgett films

Mechanisms of extrinsic and intrinsic switching phenomena in ferroelectrics are explained and existing models are summarized. Then, criteria for an experimental distinction between both models are elaborated. Samples with thicknesses ranging from 2.7 to 63.8 nm prepared by a Langmuir-Blodgett technique were investigated with respect to these criteria. Measurements of their polarization switching behaviour, their polarization hysteresis loops, and their coercive fields were carried out. It is found that the coercive fields increase with decreasing sample thickness. Also, the switching time increases with decreasing sample thickness and it increases with decreasing field strength. The switching, process turns out to be thermally activated. We find that neither intrinsic nor extrinsic models are sufficient to describe the experimental situation.