Antiferroelectrics (AFEs) possess great potential for high performance dielectric capacitors, due to their distinct double hysteresis loop with high maximum polarization and low remnant polarization. However, the well-known NaNbO₃ lead-free antiferroelectric (AFE) ceramic usually exhibits square-like P–E loop related to the irreversible AFE P phase to ferroelectric (FE) Q phase transition, yielding low recoverable energy storage density (W_rec). Herein, significantly improved W_rec up to 3.3 J/cm³ with good energy storage efficiency (η) of 42.4% was achieved in Na_0.7Ag_0.3Nb_0.7Ta_0.3O₃ (30Ag30Ta) ceramic with well-defined double P–E loop, by tailoring the A-site electronegativity with Ag⁺ and B-site polarizability with Ta⁵⁺. The Transmission Electron Microscope, Piezoresponse Force Microscope and in-situ Raman spectra results verified a good reversibility between AFE P phase and high-field-induced FE Q phase. The improved stability of AFE P phase, being responsible for the double P–E loop and improved W_rec, was attributed to the decreased octahedral tilting angles and cation displacements. This mechanism was revealed by synchrotron X-ray diffraction and Scanning Transmission Electron microscope. This work provides a good paradigm for achieving double P–E loop and high energy storage density in NaNbO₃-based ceramics.

The NaNbO₃ antiferroelectrics have been considered as a potential candidate for dielectric capacitors applications. However, the high-electric-field-unstable antiferroelectric phase resulted in low energy storage density and efficiency. Herein, good energy storage properties were realized in (1-x)NaNbO₃-xNaTaO₃ ceramics, by building a new phase boundary. As a result, a high recoverable energy density (W_rec) of 2.2 J/cm³ and efficiency (η) of 80.1% were achieved in 0.50NaNbO₃-0.50NaTaO₃ ceramic at 300 kV/cm. The excellent energy storage performance originates from an antiferroelectric-paraelectric phase boundary with simultaneously high polarization and low hysteresis, by tailoring the ratio of antiferroelectric and paraelectric phases. Moreover, the 0.50NaNbO₃-0.50NaTaO₃ ceramic also exhibited good temperature and frequency stability, together with excellent charge-discharge performance. The results pave a good way of designing new NaNbO₃-based antiferroelectrics with good energy storage performance.