Phase-field simulation of domain walls in rhombohedral ferroelectric single crystals

Domain engineered ferroelectric relaxor-PbTiO3 single crystals exhibit ultrahigh piezoelectric coefficients. A 10th order Landau-Devonshire energy function for rhombohedral PIN-PMN-PT ferroelectric single crystals was implemented in a phase-field model to study the behavior of domain walls under external electric field. The domain formation and domain wall evolution were simulated. A new way to apply periodic boundary conditions was implemented to accommodate nonzero strain during the domain formation and evolution. It was found that 71 and 109 domain walls reacted differently to external electric field along the [110] direction. A domain wall broadening effect was observed in the 71 domain walls when the electric field was below the coercive field. When the electric field exceeded the coercive field, homogeneous polarization switching occurred with no motion of the 71 domain walls. Heterogeneous polarization switching occurred by the sweeping of the 109 domain walls. The evolution mechanism of the two types of domain walls helps explain the behavior of engineered domain structures subjected to external electric field. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.