Phase field simulation of charged interface formation during ferroelectric switching

Ferroelectric switching in thin films is a local process strongly influenced by the presence and spatial distribution of defects such as dislocations, grain boundaries and preexisting domains. Preexisting ferroelastic domains have been shown to inhibit 180° switching in (001)-oriented epitaxial Pb(Zr_0.2,Ti_0.8)O₃ (PZT) films, but ferroelectric switching pathways around these domains remain unclear. Here, phase field modeling with supporting high resolution transmission electron microscopy is used to investigate ferroelectric switching in PZT thin films around such a ferroelastic domain. We show 180° domain wall motion is arrested at moderate applied biases by the ferroelastic domain through formation of charged 90° domain walls during switching. This leads to an increased applied bias required for complete switching through the thin film. Charged 90° ferroelastic domain walls are found to be partially stabilized by local rotation of the polarization direction and significant broadening of the head-to-head wall to distribute the bound charge, leading to domain walls 5-6 nm in thickness compared to 0.5-2 nm for typical 90° domain walls. Ferroelectric switching continues only at higher applied electric fields. This study provides a more complete picture of the ferroelectric switching pathway around ferroelastic domains than has been previously available and may explain the experimentally observed lower stability of written domain structures around preexisting ferroelastic domain structures in epitaxial ferroelectric thin films.