Phase transitions in ultra-thin ferroelectric films and fine period multilayers

Phase transition behaviour in ferroelectric materials is strongly dependent on boundary conditions, both electrical and mechanical. In this article, we cover several topics. Beginning with thin films, we look at the suppression of ferroelectricity as film thickness is reduced, covering two situations, the first in which the polarisation decreases and eventually is suppressed, and the second where the system forms domains in order to sustain ferroelectricity. The focus then moves to superlattices, highlighting the way that electrostatic coupling dominates the behaviour of superlattices, but revealing that for very thin layers interfacial effects can communicate through this electrostatic coupling to produce new kinds of macroscopic ferroelectric behaviour.