High energy storage density in NaNbO₃ antiferroelectrics with double hysteresis loop

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.