Ultrahigh breakdown strength achieving exceptional recoverable energy storage density in NaNbO₃-based lead-free dielectrics

Dielectric ceramic capacitors have attracted significant interest in advanced pulsed power systems owing to their ultrahigh power density and fast charge/discharge capabilities. The low breakdown strength (Eb) of dielectric ceramics poses a major bottleneck for achieving high recoverable energy storage density (Wrec). In this study, using ingenious chemical component design, we achieved an ultrahigh Eb of 800 kV/cm and an excellent Wrec value of 9.48 J/cm3 in the simple component 0.92NaNbO3–0.08SmFeO3 ceramic. Finite element simulations corroborate that the optimized grain boundary network enables more uniform electric field distribution and effective suppression of breakdown propagation. The superior energy storage characteristics originate from two synergistic mechanisms: (Ι) the incorporation of SmFeO3 suppresses grain growth, resulting in refined microstructure with increased grain boundary density that substantially enhances Eb; (II) the introduction of Sm3+ and Fe3+ ions causes a mismatch between the A/B site ions, inducing lattice distortion and high disorder, which enhances the local random fields and relaxor behavior. This study establishes a promising pathway for designing high-energy-density dielectric ceramic capacitors.