The effect of misfit dislocations upon the statics and dynamics of 90° domains (twins) in epitaxial thin films was studied theoretically. The misfit dislocations created additional potential barriers which hindered the movement of domain walls along the film/substrate interface. In the case of ferro-elastic 90° walls, these barriers were high because an elastic interaction existed between 90° domains and misfit dislocations; due to coupling of the dislocation stresses to spontaneous strains that were generated at the proper or improper ferro-elastic phase transition. The energy of elastic interaction was evaluated for a single 90° domain which was embedded in a tetragonal film that contained a periodic array of edge misfit dislocations. The equilibrium width of a single embedded 90° domain was then calculated as a function of the misfit strain in the film/substrate system. It was found that, at a threshold value of the misfit strain, gradual variations in the domain width were interrupted by step-like changes. The evolution of the 90° domain pattern during polarization switching in ferro-electric films with misfit dislocations was analyzed. The results showed that the electric field-induced growth of an embedded 90° domain involved 3 different stages. At a critical value of the applied electric field, one of the 90° domain walls could even jump over the neighboring misfit dislocation. This was accompanied by abrupt changes in the domain width, and its position in the film. The step-like movements of 90° domain walls over the misfit dislocations were proposed to be a possible microscopic mechanism for the Barkhausen effect in ferro-electric thin films during polarization reversal. An hysteretic behavior of 90° domains under cyclic variations of an applied electric field was demonstrated.

Abrupt Changes and Hysteretic Behavior of 90° Domains in Epitaxial Ferroelectric Thin Films with Misfit Dislocations. A.Y.Emelyanov, N.A.Pertsev: Physical Review B, 2003, 68[21], 214103 (10pp)