Nucleation, pinning and hysteresis effects at the incommensurate-commensurate transition

Abstract

Thermal hysteresis effects due to nucleation and pinning of two- and three-dimensional incommensurate structures are considered at the IC transition and inside the incommensurate phase. A possible disorder-induced domain wall interaction is taken into account. Various equilibrium and non-equilibrium effects due to randomly frozen-in impurities are critically summarised. The results allow the interpretation of unusual hysteresis effects of the dielectric constant observed recently in improper ferroelectrics. It is argued that nucleation is the decisive mechanism for the change of the domain wall density in incommensurate systems.