First-order morphological transition of ferroelastic domains in ferroelectric thin films

Ferroelastic domains are common defects in epitaxial ferroelectric thin films, being typically observed around interfacial dislocations due to attractive elastic interactions. Because of their large stress fields, domain size and shape can influence local ferroelectric switching behavior. Here the morphology of ferroelastic domains in Pb(Zr_0.2, Ti _0.8)O₃ thin films is investigated as a function of film thickness and substrate strain using phase field modeling in combination with transmission electron microscopy. Increasing film thickness or strain is found to induce switching from typical ferroelastic domains extending to the free surface of the film to nanosized domains localized near the substrate interface. An analysis of thermodynamic properties reveals hysteretic and discontinuous changes in the first derivatives of the free energy resulting from competing electrostatic and elastic energies. Such first-order morphological transitions are expected to be very common in epitaxial thin films during switching under an external electric or stress field.