Influence of depolarization field on temperature-misfit strain phase diagram of PbZr_0.4Ti_0.6O₃ultrathin films

Phase-field simulations are performed to study domain structures in (001)-oriented PbZr0.4Ti0.6O3 epitaxial thin films. Temperature-misfit strain phase diagrams of the domain structures are constructed under various depolarization fields by adjusting surface screening conditions and film thickness. We find that the vortex-array state area in the phase diagram enlarges with the decrement of the depolarization field, which is contrary to the general view of depolarization field conductive to vortex formation. Moreover, a strain-mediated ferroelectric failure mechanism is found, wherein the ferroelectric characteristics of an ultrathin film with a thickness of 4 nm completely disappear (Curie temperature drops to 0 K) under the open-circuit condition when the compressive misfit strain drops to -2.69%. The results guide further understanding and manipulation of domain structures in ferroelectric nanomaterials.