Large-signal analysis of typical ferroelectric domain structures using phase-field modeling

Domain structures as typically found in tetragonally polarized ferroelectrics are investigated regarding their large-signal behavior by conducting phase-field simulations. The underlying free energy function of the phase-field model stems from a completely knowledge-based multiscale adjustment approach (Völker et al 2011 Contin. Mech. Thermodyn. 23 435–451) and is based on results from atomistic DFT calculations and SMP simulations. We address the question of whether phase-field models in such a multiscale simulation approach are capable of yielding reasonable values for the coercive electric field strength, i.e. the electric fields necessary to initiate irreversible switching processes in the domain structure, causing the experimentally observed hysteresis behavior of ferroelectrics. Therefore, a variety of typical ferroelectric bulk domain structures are taken into account and studied regarding their large-signal behavior. Trends are shown in the correlation between the complexity of the domain structure and the coercive field strength predicted by the phase-field model. The role of imperfections in the material such as charged defects and grain boundaries is of special interest, since they act as nucleation centers for new domains under electric loading. In this way, they reduce significantly the coercive field strength from the value given by the energy barrier in the free energy to magnitudes close to or of the order observed in experiments on polycrystalline ferroelectrics. (paper)