Stepwise-design activated high capacitive energy storage in lead-free NaNbO3-based relaxor antiferroelectric ceramics

Although comparable energy storage performance (ESP) has been realized in NaNbO3 (NN)-based antiferroelectric (AFE) ceramics, how to simultaneously realize large energy density (Wrec), large storage efficiency (eta), and outstanding thermal stability still remains a remarkable challenge. Herein, by progressively substituting BiFeO3 (BF) and CaTiO3 (CT), we propose a stepwise-design strategy to activate comprehensive exceptional ESP in NN-based relaxor AFE ceramics. The substitution of BF with high spontaneous polarization and CT with high breakdown strength (Eb) into NN generates stabilized AFE R phase, strong tilt distortions of oxygen octahedron, ultrasmall and highly dynamic polar nanoregions, and refined grains, thus manifesting enhanced high-field polarizability, significantly delayed polarization saturation, and ultrahigh Eb macroscopically. With the deliberate stepwise-design route, we realize an optimal overall ESP in 0.6(0.96NN-0.04BF)-0.4CT relaxor AFE ceramics, featuring a high Wrec of 6.84 J/cm3, a large eta of 81.5 %, along with super temperature/frequency/fatigue stabilities, which shows great performance merits compared with previous reports. This work demonstrates that stepwise-design engineering approach by manipulating the crucial structures exerts a positive size effect on the polarization and breakdown response of dielectrics, and can be exploited for designing more high-performance energy storage ceramics.