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 (Wrec). Herein, significantly improved Wrec up to 3.3 J/cm3 with good energy storage efficiency (η) of 42.4% was achieved in Na0.7Ag0.3Nb0.7Ta0.3O3 (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 Wrec, 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.