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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]

• Achieving ultrahigh W rec of 10.0 J/cm3 and η of 91 % in BST-based ceramics. • The variation of relaxor feature is analyzed by multi-polarization mechanism model. • Simultaneously toughening and enhanced energy storage performance are realized. Lead-free ceramic capacitors offer ultrahigh power density and ultrafast discharging rates, making them critical energy storage components for advanced pulsed power systems. However, the greatest obstacle to broader applications remains the relatively low energy storage density. In this study, a relaxor ferroelectric ceramic based on (0.6-x)Ba 0.55 Sr 0.45 TiO 3 -0.4Bi 0.5 Na 0.5 TiO 3 -xSrZrO 3 ((0.6-x)BST-0.4BNT-xSZ) is prepared using the tape casting method, resulting in an excellent energy density (W rec ≈ 10.0 J cm−3) and high energy storage efficiency (η ≈ 91 %). The solid solution of linear dielectrics SrZrO 3 synergistically regulates both relaxor properties and breakdown strength. The variation of relaxor property was explored utilizing New Glass model and the multi-polarization model, with confirmation provided by piezoresponse force microscopy. Furthermore, the breakdown strength could be attributed to improvements in electric insulation and the widening of the bandgap. As SrZrO 3 content increases, the in-situ emergence of the second phase ZrO 2 , accompanied by a martensitic transformation, not only improves the fracture toughness of ceramics but also serves to elongate the breakdown path. Encouragingly, x = 0.20 ceramics also achieve excellent temperature stability (−95–125 ℃), frequency stability (1–1000 Hz), cycling reliability (1–106 cycles), and great charging-discharging properties. This multiscale synergic regulation strategy plays a guiding role in the screening of high-performance energy storage dielectric materials. [ABSTRACT FROM AUTHOR]

• The composite ceramics Bi 0.5 Na 0.5 TiO 3 -Sm 2 Ti 2 O 7 were successfully prepared. • Excellent electrical properties and stability are obtained in BNT-STO ceramics. • A new effective method to design high ESP ceramic materials is proposed. The comprehensive performance of ferroelectric ceramic materials is a significant factor limiting the practical application. In this work, a novel strategy of constructing diphase compounds is proposed to significantly enhance the energy storage properties of Bi 0.5 Na 0.5 TiO 3 -based ceramics. A composite ceramic of pyrochlore phase Sm 2 Ti 2 O 7 modified perovskite phase Bi 0.5 Na 0.5 TiO 3 is successfully prepared and systematically studied. As the concentration of Sm 2 Ti 2 O 7 increases, the dielectric breakdown strength is greatly strengthened because of expanded band gap and shrunk grain size, and the relaxor behavior is enhanced due to the effect of linear character pyrochlore. As a result, the optimized composition demonstrates excellent energy storage properties including high recoverable energy storage density (W rec) of 6.387 J/cm3 at 402 kV/cm, superior stability of temperature (<6% variation in − 120 ∼ 120 °C), frequency (∼4% variation in 5 ∼ 500 Hz) and cycling (∼2% variation within 106 cycles). Besides, fast discharge behavior of t 0.9 ∼ 29.4 ns and high power density of 80.49 MW/cm3 at 200 kV/cm are also achieved. This study presents a novel strategy to enhance the performance of BNT-based materials through forming composite ceramic, which is anticipated to be a general method for other material systems as regards the design of advanced energy storage ceramics. [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]