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_0.5Na_0.25K_0.25)TiO₃ ferroelectric and paraelectric BaZrO₃ 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.