Electric-field-induced antiferroelectric to ferroelectric phase transition in polycrystalline NaNbO3

Electric-field-induced phase transitions are the most important characteristics of antiferroelectric materials. However, in several prototype antiferroelectrics, these transitions are irreversible and the origin of this behavior is poorly understood. This prevents their widespread use, for example, in energy storage and memory applications. Here, we investigated the antiferroelectric-ferroelectric phase transitions in polycrystalline NaNbO3, a material recently suggested as the basis for lead-free antiferroelectrics with high energy storage densities. An irreversible transition from the antiferroelectric state to a new state showing macroscopic piezoelectricity (d(33)=35 pC/N) was induced at 11.6 kV/mm (room temperature, 1 Hz), accompanied by a 33% drop in permittivity. Microscopically, a change from a translational antiferroelectric domain structure to a wedge-shaped ferroelectric domain structure was observed using transmission electron microscopy. Na-23 solid-state nuclear magnetic resonance allowed for a detailed study of the local structure and revealed pure antiferroelectric and coexisting antiferroelectric/ferroelectric nature of the samples before and after the application of an electric field, respectively. Interestingly, despite the large electric fields applied, only 50 +/- 5% of the material underwent the antiferroelectric-ferroelectric phase transition, which was related to the materials microstructure. The temperature- and frequencydependence of the phase transition was studied and compared to the behavior observed in lead-based antiferroelectric systems. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.