Superior Capacitive Energy Storage in Lead‐Free Bi 0.5 Na 0.5 TiO 3 ‐based Relaxors via High‐Entropy Design

ABSTRACT Dielectric capacitors are attractive for the high/pulsed power electronic systems owing to their ultrafast charging/discharging capability. Yet, the simultaneous achievement of high recoverable energy density ( W rec ) and efficiency ( η ) in lead‐free relaxor ferroelectric (RFE) ceramics still remains a major challenge. Here, a high‐entropy engineering in Bi 0.5 Na 0.5 TiO 3 ‐based RFE ceramics was proposed to construct heterogenous local structures, demonstrating an ultrahigh W rec of 13.7 J cm −3 and a high η of 86% under 780 kV cm −1 . Atomic‐scale microstructure, along with the three‐dimensional polar structure derived from neutron total scattering, revealed that the diversified A‐site atoms increase the local chemical heterogeneity and lattice distortion of AO 12 cages, facilitating the formation of strong local clusters distributed in the matrix with weak polarity, thereby yielding enhanced relaxor behavior, reduced polarization hysteresis, and retained high polarization after applying an electric field. Moreover, the promoted insulating performance and significant reduced grain size result in a high endurance for external electric field. This work elucidates the roles of A‐site atoms in the high‐entropy effect, local lattice distortion, atomic polar displacement and energy storage properties, offering insights for the design of complex ferroelectrics with high‐performance.