Synergistic regulation of lattice disorder and polar nanoregions through an antiferroelectric-to-relaxor transition in (1−x)NaNbO3–xSr0.7Bi0.2TiO3 ceramics for enhanced energy storage performance

Lead-free dielectric ceramics exhibiting both high recoverable energy density and ultrahigh efficiency are critically sought for advanced pulsed power applications; however, achieving these properties remains challenging due to inherent trade-offs among polarization difference, energy loss, and breakdown strength in conventional antiferroelectric systems. In this work, (1− x )NaNbO 3 – x Sr 0 . 7 Bi 0 . 2 TiO 3 [(1− x )NN– x SBT] ceramics were successfully synthesized via a conventional solid-state method, and the composition–structure–property relationships were systematically elucidated. Structural characterizations indicate that increasing the SBT content induces a continuous transition from long-range antiferroelectric ordering to a relaxor state, accompanied by enhanced lattice disorder and the formation of polar nanoregions (PNRs), as confirmed by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM) analyses. Concurrently, significant grain refinement and improved microstructural homogeneity effectively enhance the breakdown strength. Consequently, the polarization behavior evolves from hysteretic domain switching to highly reversible PNR-dominated responses, resulting in markedly suppressed remnant polarization and an increased polarization difference (Δ P ). As a result, the optimized compositions exhibit outstanding energy-storage performance, with a maximum recoverable energy density ( W rec ) of 8.17 J/cm 3 obtained at x  = 0.7 and an ultrahigh energy-storage efficiency ( η ) of 99.8% achieved at x  = 0.8 under a high breakdown strength of 620 kV/cm. Furthermore, the optimized ceramics exhibit excellent thermal stability over 20–140 °C, robust fatigue endurance up to 10 5 cycles, and ultrafast discharge characteristics with a t 0.9 of approximately 50 ns, together with a high-power density. These superior performances are attributed to the synergistic effects of PNR-dominated dynamic polarization, suppressed long-range antiferroelectric ordering, and refined microstructure. This work provides a clear strategy for designing high-performance lead-free NaNbO 3 -based dielectric capacitors through coordinated structural disorder and nanoscale polarization engineering.