Dielectric energy-storage capacitors have received increasing attention in recent years due to the advantages of high voltage, high power density, and fast charge/discharge rates. Here, a new environment-friendly 0.76NaNbO 3 -0.24(Bi 0.5 Na 0.5 )TiO 3 relaxor antiferroelectric (AFE) bulk ceramic is studied, where local orthorhombic Pnma symmetry (R phase) and nanodomains are observed based on high-resolution transmission electron microscopy, selected area electron diffraction, and in/ex situ synchrotron X-ray diffraction. The orthorhombic AFE R phase and relaxor characteristics synergistically contribute to the record-high energy-storage density W rec of ≈12.2 J cm −3 and acceptable energy efficiency η ≈ 69% at 68 kV mm −1 , showing great advantages over currently reported bulk dielectric ceramics. In comparison with normal AFEs, the existence of large random fields in the relaxor AFE matrix and intrinsically high breakdown strength of NaNbO 3 -based compositions are thought to be responsible for the observed energy-storage performances. Together with the good thermal stability of W rec (>7.4 J cm −3 ) and η (>73%) values at 45 kV mm −1 up to temperature of 200 °C, it is demonstrated that NaNbO 3 -based relaxor AFE ceramics will be potential lead-free dielectric materials for next-generation pulsed power capacitor applications.

Dielectric capacitors are receiving a great deal of attention for advanced pulsed power owing to their high power density and quick charge/discharge rate. However, the energy density is limited and the efficiency and the thermal stability are also not ideal, which has been a longstanding obstacle to developing desirable dielectric materials. These concerns have are addressed herein by fabricating nanodomain‐engineered BiFeO3‐BaTiO3‐NaNbO3 bulk ferroelectrics, integrating a high‐spontaneous‐polarization gene, wide band gaps, and a heterogeneous nanodomain structure, generating record‐excellent comprehensive performance of giant energy‐storage density Wrec ≈8.12 J cm−3, high efficiency η ≈90% and excellent thermal stability (±10%, −50 to 250 °C) and ultrafast discharge rate (t0.9 < 100 ns). Significantly enhanced dielectric breakdown strength of BiFeO3‐based solid solutions is mainly attributed to the substitution of NaNbO3, which provides an increased band gap, refined grain size, and increased resistivity. The formation of nanoscale domains as evidenced by piezoresponse force microscopy and transmission electron microscopy enables nearly hysteresis‐free polarization‐field response and temperature‐insensitive dielectric response. In comparison with antiferroelectric capacitors, the current work provides a new solution to successfully design next‐generation pulsed power capacitors by fully utilizing relaxor ferroelectrics in energy‐storage efficiency and thermal stability.

A novel lead-free polar dielectric ceramic with linear-like polarization responses was found in (1 − x)(Bi0.5Na0.5)TiO3–xNaNbO3 ((1 − x)BNT–xNN) solid solutions, exhibiting giant energy storage density/efficiency and super stability against temperature and frequency.

Next-generation advanced high/pulsed power capacitors rely heavily on dielectric ceramics with high energy storage performance. However, thus far, the huge challenge of realizing ultrahigh recoverable energy storage density (Wrec) accompanied by ultrahigh efficiency (η) still existed and has become a key bottleneck restricting the development of dielectric materials in cutting-edge energy storage applications. Here, we propose a high-entropy strategy to design “local polymorphic distortion” including rhombohedral-orthorhombic-tetragonal-cubic multiphase nanoclusters and random oxygen octahedral tilt, resulting in ultrasmall polar nanoregions, an enhanced breakdown electric field, and delayed polarization saturation. A giant Wrec ~10.06 J cm−3 is realized in lead-free relaxor ferroelectrics, especially with an ultrahigh η ~90.8%, showing breakthrough progress in the comprehensive energy storage performance for lead-free bulk ceramics. This work opens up an effective avenue to design dielectric materials with ultrahigh comprehensive energy storage performance to meet the demanding requirements of advanced energy storage applications.

Lead‐free dielectric ceramics with ultrahigh energy storage performance are the best potential stocks used in next‐generation advanced pulse power capacitors. Here, an ultrahigh recoverable energy storage density Wrec of ≈7.57 J cm−3 and a large efficiency η of ≈81.4% are first realized in (Bi0.5K0.5)TiO3 (BKT)‐based relaxor ferroelectric ceramics with an ultrahigh Vickers hardness Hv ≈ 8.63 Gpa by adding BaTiO3 and NaNbO3 in order to synergistically design the domain and microstructure in multiscale, leading to the existence of ultrasmall polar nanoregions, ultrafine grain size, compact grain boundaries, dense microstructure, and large band gap Eg simultaneously. Encouragingly, an excellent energy storage temperature stability (Wrec ≈ 4.31 ± 0.25 J cm−3, η ≈ 86 ± 5%, 20–200 °C), frequency stability (Wrec ≈ 5.14 ± 0.12 J cm−3, η ≈ 81.3 ± 1.2%, 5–100 Hz), and excellent charge/discharge performance (power density PD ≈ 103.2 MW cm−3, discharge energy density WD ≈ 2.4 J cm−3, discharge rate t0.9 ≈ 130 ns) are also achieved in BKT‐based ceramics. The results demonstrate that BKT‐based ceramics can be very competitive lead‐free relaxors for energy storage capacitors in pulsed power devices.

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The combination of AFE phase structural regulation and breakdown strength optimization through chemical modification leads to a large energy-storage density of Wrec ∼ 5.57 J cm−3 in NN–BMT lead-free bulk ceramics.