High‐Entropy Superrelaxor State Engineering toward Exceptional Capacitive Energy Storage in Lead‐Free Ceramics under Moderate Electric Field

ABSTRACT Although lead‐free dielectric ceramics have achieved ultra‐high energy storage performance (ESP) under extreme electric fields ( E > 500 kV/cm), operation within the moderate electric field range (300 kV/cm ≤ E ≤ 500 kV/cm) is the most crucial and reliable for practical pulsed power applications. Unfortunately, simultaneously achieving high recoverable energy storage density ( W rec > 8 J/cm 3 ) and efficiency ( ƞ > 90%) under moderate electric field remains a challenge. Herein, (1‐ x )(Ba 0.3 Sr 0.7 ) 0.35 (Bi 0.5 Na 0.5 ) 0.65 TiO 3 ‐ x SrHfO 3 (BNBST‐ x SH) ceramics are designed through high‐entropy (HE) superrelaxor state engineering to optimize their ESP. As the x value increases, configurational entropy rises, inducing phase competition and stabilizing the superrelaxor state at room temperature. The HE environment disrupts long‐range ferroelectric order and promotes random octahedral tilting. Additionally, the superrelaxor state enables the coexistence of long‐range disordered weakly polar and short‐range ordered polar structures. Consequently, an excellent W rec of 8.13 J/cm 3 with a high ƞ of 91.67% is obtained in BNBST‐0.20SH ceramic under a moderate electric field of 425 kV/cm, which also exhibits robust ESP stability and ultra‐fast charging‐discharging speed. This work provides an effective strategy for enhancing the ESP of lead‐free dielectric ceramics under moderate electric field and offers a promising material for applications in integrated industrial systems.