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• An ever-unadoped strategy was employed to design superparaelectric phase in AgNbO 3. • A new simple composition to obtain high ESP ceramic materials is proposed. • High W rec of 7.6 J/cm3 and E b of 522 kV/cm are obtained. Ceramics capacitors, especially featuring antiferroelectric (AFE) structure, are widely used in pulsed power electronic systems due to distinctive high-power density and external field stability. Lead-free AFE material AgNbO 3 has seized substantial research attention owing to its unique temperature driven multi-level phase transitions, and many works have greatly improved the energy storage properties by engineering these temperature-dependent phase boundaries. In this work, an ever-unadopted strategy was proposed to modulate the relaxor structure in AgNbO 3 by designing room-temperature (RT) superparaelectric phase via Bi incorporation into AN lattice matrix. Structural analysis shows M phase (space group Pbcm) evolves into O phase (space group Cmcm) with 12 mol.% Bi-substitution, breaking the long-range AFE order into polar nanoregions. Hence, an ultra-high recoverable energy density (7.6 J/cm3) and a high efficiency (79 %) are simultaneously achieved in the Ag 0.64 Bi 0.12 NbO 3 ceramics under 52.2 kV/mm. Moreover, the excellent energy storage properties are accompanied with good temperature and frequency stability, with the variation of W rec less than ± 15% (over 25–120 °C) and ± 10% (over 1–200 Hz) under 25 kV/mm, respectively. The novel approach reported herein provides a new guidance for designing AgNbO 3 -based and other AFE materials for high-performance energy storage applications. [ABSTRACT FROM AUTHOR]

• The comprehensive optimization strategy of discharge curve can serve as the paradigm of conceptual materials. • A balance between W re = 5.92 J/cm3 and η = 81.7% is gotten in the BSZT-BMN-0.06 ceramic. • The mechanism of core–shell structure enhancing breakdown strength is clarified. • BSZT-BMN-0.06 ceramics owns a fast charge–discharge speed (44 ns) and a high P D of 144 MW/cm3. The conventional dielectric ceramics are extensively studied for applications in electronics and pulsed power systems owing to the advantages of high voltage and high power density. However, the inferior energy storage performance is difficult to satisfy the development requirements of integration and lightweight of power electronic devices. The main research efforts have been done to improve the energy storage density by enhancing the electric breakdown strength (BDS) or effective dielectric constant (ΔP/ΔE) due to the contradiction between ΔP/ΔE and BDS. Here, it is proposed to use composition design and microstructural core–shell engineering to surmount this contradiction and thus enhance the energy storage density. The heterogeneous microstructures are introduced through a two-step calcination, and the appearance of this microstructure is related to the destruction of the cooperative diffusion effect of multiple ions. Consequently, 0.93Ba 0.55 Sr 0.45- x Zn x TiO 3 -0.07BiMg 2/3 Nb 1/3 O 3 (BSZT-BMN- x) ceramics with core–shell microstructure prepared by traditional solid-state reaction method exhibits an ultrahigh recoverable energy density of 5.92 J/cm3, a superior energy storage efficiency of 81.7% and an outstanding charge–discharge performance (P D = 144 MW/cm3, t 0.9 = 44 ns). The experimental results and numerical simulations reveal that the doping of Zn2+ enhances the potential for off-centering of anions and cations, the core–shell microstructure makes the distribution of electric field to be regulated and the effective path of electric trees is extended to improve the BDS. The present research not only offers a novel paradigm for other material systems to further improve energy storage performance, but also should be generalizable for other functional materials for which a high BDS is required. [ABSTRACT FROM AUTHOR]