Adaptive Local and Global Structure Enabling Superior Capacitive Energy‐Storage in Pb‐Free Relaxors Under Moderate Electric Field

Pb‐free relaxor ferroelectric (RFE)‐based dielectric capacitors have great potential in cutting‐edge pulsed‐power/high‐power systems. Particularly, a high energy density ( W rec ) under a moderate electric‐field ( E ) is urgent for electric vehicles and advanced electronic devices. However, achieving this, such as overcoming the bottleneck of W rec > 10 J cm −3 under E ≤ 60 kV mm −1 , remains challenging owing to trade‐off between critical parameters. Herein, an adaptive local‐global structure tactic is presented to obtain large and high‐reversible polarizability, and realizing a record‐high W rec of 12 J cm −3 and a high efficiency ( η ) of 89% among Pb‐free bulk ceramics under moderate E . This is implemented by combining the strong distorted (Bi 0.5 Na 0.25 K 0.25 )TiO 3 ferroelectric and paraelectric BaZrO 3 to form global tolerance factor optimized solid‐solutions. Locally, such RFE state exhibits fluctuating atomic displacement vectors, featured by a broad range of magnitudes and orientations, and forming strongly polarizable and small‐sized clusters. It results in a record‐high reversible polarizability and large polarization difference of 56.3 µC cm −2 under 56 kV mm −1 . Furthermore, the excellent reliability, high discharge energy density (4.5 J cm −3 ), and large power density (504.5 MW cm −3 ) are obtained. These results demonstrate the feasibility of adaptive local‐global structure in enhancing the energy‐storage capabilities under moderate E .