Achieving ultrahigh energy storage density under low electric field in (Na0.5Bi0.5)TiO3-based relaxor ferroelectric ceramics via a synergistic optimization strategy

Lead-free dielectric ceramic capacitors are attracting much interest in pulse power systems owing to their fast charge/discharge rate and high power density. However, their development towards integration and miniatur-ization in electronic devices has been severely impeded by low energy storage performance (ESP) under low electric field (E). Herein, a synergistic optimization strategy of composition design and domain engineering was proposed in the Bi(Mg0.5Hf0.5)O3-modified Na0.5Bi0.5TiO3-Sr0.7Bi0.2Ca0.1TiO3 ceramics [(1-x)(NBT-SBCT)-xBMH], aiming to improve ESP at low E. As a result, an ultrahigh recoverable energy density (Wrec) of-5.9 J/ cm3 and a high efficiency (eta) of-85 % can be obtained in x = 0.20 ceramics under a low E of 260 kV/cm, which is superior to previously reported lead-free materials under the equivalent E. The outstanding Wrec is mainly ascribed to the ultrahigh polarization discrepancy (Delta P) of-50.8 mu C/cm2 since the rich hybridization of Bi 6 s and O 2p orbitals maintains a maximum polarization and the addition of Mg2+ and Hf4+ transforms the long-range ferroelectric order into polar nanoregions (PNRs) with good relaxation characteristics. Moreover, a fast discharge time (-62 ns), good temperature (20-120 degrees C) and frequency (1-103 Hz) stabilities, and excellent fatigue resistance (x105 cycles) can be concurrently realized in x = 0.20 ceramics. These results demonstrate the promising strategy of developing low E lead-free ceramics for dielectric energy storage.