High capacitive energy-storage in BNT-based Pb-free relaxors via dispersing strong long-range polarization within expanded lattice framework

The development of Pb-free dielectric materials with high recoverable energy-storage density (Wrec) and efficiency (η) remains a critical challenge for cutting-edge pulsed-power technologies. Herein, we propose a rational structural and chemical design to stabilize a relaxor state with tolerance factor t = 1.0096 by coupling highly distorted ferroelectric matrix with lattice-expanded component. We can disperse the strong long-range polarization within an expanded lattice framework through incorporating BaSnO3 into Bi0.5Na0.5TiO3-BaTiO3 solid-solution with significant ferroelectric polarization, thereby achieving a synergistic optimization between the large intrinsic polarization and lattice structure. Neutron total scattering combined with Reverse Monte Carlo modeling, and atomic-resolution displacement mapping reveal Sn4+ disrupts strong long-range polarization via B-site chemical frustration, generating polar nanoclusters with intense local distortions. Concurrently, Ba2+-driven lattice expansion enhances polarization flexibility under electric fields. Notably, Bi3+-enriched nanoregions retain unit-cell polarization up to 60 μC·cm-2, confirming the coexistence of relaxor dynamics and strong local polar fluctuations. The optimized ceramic exhibits slim hysteresis loops with exceptional energy-storage performance (Wrec = 11 J·cm-3, η = 85%), and excellent charge-discharge behavior (WD = 7.0 J·cm-3 and PD = 688 MW·cm-3). This work establishes a paradigm for correlating microstructure and performance in Pb-free relaxors with high capacitive energy-storage.