Reversible electric-field-induced phase transition in Ca-modified NaNbO(3) perovskites for energy storage applications

Sodium niobate (NaNbO(3)) is a potential material for lead-free dielectric ceramic capacitors for energy storage applications because of its antipolar ordering. In principle, a reversible phase transition between antiferroelectric (AFE) and ferroelectric (FE) phases can be induced by an application of electric field (E) and provides a large recoverable energy density. However, an irreversible phase transition from the AFE to the FE phase usually takes place and an AFE-derived polarization feature, a double polarization (P)-E hysteresis loop, does not appear. In this study, we investigate the impact of chemically induced hydrostatic pressure (p(chem)) on the phase stability and polarization characteristics of NaNbO(3)-based ceramics. We reveal that the cell volume of Ca-modified NaNbO(3) [(Ca(x)Na(1−2x)V(x))NbO(3)], where V is A-site vacancy, decreases with increasing x by a positive p(chem). Structural analysis using micro-X-ray diffraction measurements shows that a reversible AFE–FE phase transition leads to a double P-E hysteresis loop for the sample with x = 0.10. DFT calculations support that a positive p(chem) stabilizes the AFE phase even after the electrical poling and provides the reversible phase transition. Our study demonstrates that an application of positive p(chem) is effective in delivering the double P-E loop in the NaNbO(3) system for energy storage applications.