Multi-scale structure regulation of bismuth sodium titanate-based ceramics for high energy storage performance under medium electric field

Lead-free Na_0.5Bi_0.5TiO₃ (NBT)-based relaxor ferroelectrics (RFEs) have emerged as promising candidates for energy storage applications owing to their superior polarization characteristics and tunable relaxor behavior. Nevertheless, their relatively low recoverable energy storage density (W_rec) has significantly hindered practical implementation. In this study, we developed a novel NBT-STA-xSm ceramic system by incorporating polar nanoregions (PNRs) into a multiphase-coexisted matrix while in- situ forming a secondary phase with both high resistivity and high intrinsic breakdown strength (E_b). Remarkably, the optimal composition with x = 0.08 demonstrates exceptional energy storage performance, achieving an ultrahigh W_rec of 13.14 J/cm³ and an energy efficiency (η) of 80.03% under an applied electric field of 470 kV/cm. This outstanding performance originates from the synergistic effect of an exceptionally large polarization difference (ΔP=P_max-P_r) and enhanced E_b. The achieved performance also exhibits excellent stability: the W_rec variation remains within ±3% across a temperature range of 20–120 °C, while the η fluctuation is maintained less than ±5% even after 2 × 10⁵ charge-discharge cycles within a frequency range of 1–500 Hz. This work establishes a new paradigm for designing high-performance lead-free energy storage dielectrics, with comprehensive properties that satisfy the rigorous demands of modern capacitor applications in terms of energy density, efficiency, and reliability.