Entropy‐Driven Polarization Disordering Enables Ultrahigh Energy Storage Performance in Lead‐Free Ferroelectric Ceramics

ABSTRACT Dielectric capacitors are critical for modern power electronics, yet achieving high recoverable energy density ( W rec ) and efficiency simultaneously remains challenging. [Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ]TiO 3 (BNKT) exhibits strong ferroelectric order with large remanent polarization and moderate breakdown strength, limiting practical performance. Here, an entropy‐driven design is implemented via stepwise heterovalent doping at A‐ and B‐sites. Partial substitution with NaNbO 3 disrupts long‐range ferroelectric order, generating polar nanoregions (PNRs), reducing remanent polarization, and enhancing breakdown strength. Subsequent Sr(Nb 0.5 Al 0.5 )O 3 incorporation further increases chemical disorder and lattice distortion, forming a dense network of PNRs that reorient rapidly and reversibly under electric fields. The optimized (1– x )[0.74Bi 0.51 (Na 0.82 K 0.18 ) 0.5 TiO 3 ‐0.26NaNbO 3 ]‐ x Sr(Nb 1/2 Al 1/2 )O 3 ceramics achieve a W rec of 12.6 J cm −3 with 88.8% efficiency, while maintaining W rec = 6.3–7.1 J cm −3 over 1–200 Hz, 5.6–6.5 J cm −3 from 30°C–140°C, and negligible change after 1.1 × 10 5 fatigue cycles. These results demonstrate that entropy‐driven polarization disorder enables simultaneous optimization of energy density, efficiency, and breakdown strength, providing a generalizable strategy for lead‐free high‐performance dielectric capacitors.