(Bi_0.5Na_0.5)TiO₃–NaNbO₃–Bi(Mg_1/2Zr_1/2)O₃ Lead-Free Relaxor Antiferroelectric Ceramics Featuring Ultrahigh Temperature-Insensitive Energy-Storage Performance

The development of lead-free dielectric ceramics with superior energy-storage performance is critical for next-generation pulsed-power capacitors. This work presents a breakthrough in lead-free (0.8- x )(Bi 0.5 Na 0.5 )TiO 3 –0.2NaNbO 3 – x Bi(Mg 1/2 Zr 1/2 )O 3 relaxor antiferroelectric ceramics featuring temperature-insensitive antipolar nanoregions with P 4 bm symmetry, as confirmed by ex- and in situ XRD, Raman spectroscopy, and TEM analysis. In-situ piezoresponse force microscopy demonstrates the electric-field-driven reversible transformation between the antipolar nanoregions and ferroelectric microdomains, accompanied by rapid recovery kinetics upon field removal. This behavior enables a linear-like polarization-field response with minimal hysteresis. Moreover, the synergistically improved grain morphology and band structure contribute to a significantly enhanced breakdown strength. As a result, a superb recoverable energy density W rec ≈ 8.6 J/cm 3 and a high energy efficiency η ≈ 85.5% are simultaneously achieved under 55 kV/mm in the x = 0.20 composition, which also exhibit a remarkable thermal stability ( W rec = 4.2 ± 1.7% J/cm 3, η = 84.9 ± 4.0%, 20–260 °C) and ultrafast charge–discharge capabilities (Powder density P D = 264.7 MW/cm 3, discharge energy density W D = 5.1 J/cm 3, discharge time t 0.9 < 30 ns). These findings demonstrate a promising strategy for exploiting lead-free dielectrics with desirable overall energy-storage features for capacitor applications.