High-entropy and phase engineering towards excellent energy storage performance in lead-free Bi0.5Na0.5TiO3-based ceramics under moderate electric fields

Abstract

While the high-entropy (HE) strategy has enabled lead-free dielectric ceramics to achieve ultra-high energy storage performance (ESP) under extreme electric fields ( E > 500 kV/cm), their ESP at moderate field fields (200 kV/cm ≤ E ≤ 500 kV/cm) remains restricted by the trade-off between breakdown strength ( E b ) and polarization difference (Δ P ), limiting their practical industrial applications. Herein, (1- x )(Bi 0.5 Na 0.5 ) 0.65 (Ba 0.3 Sr 0.7 ) 0.35 TiO 3 - x Ca(Mg 1/3 Ta 2/3 )O 3 (BNBST- x CMT) ceramics are designed via HE strategy and phase engineering to optimize their ESP. Introducing CMT into the BNBST ceramics elevates configuration entropy, facilitates the reversibility of polarization switching, and induces phase competition. The highest weak-polar phase fractions with the small domain size in BNBST-0.15CMT ceramic effectively delay polarization saturation while maintaining a large polarization response at maximum electric fields. Furthermore, the E b is enhanced by improvements in the optical band gap, electrical homogeneity, and overall insulation characteristics, indicating the average grain size is not the only factor to determine E b . Consequently, the BNBST-0.15CMT ceramic achieves a favorable W rec of 4.81 J/cm 3 with a high ƞ of 84.68% at 340 kV/cm, alongside exceptional ESP stability and ultra-fast charging-discharging rate ( t 0.9 = 33.8 ns). This work offers an effective methodology to optimize the ESP of lead-free dielectrics under moderate electric fields.