Superior Energy‐Storage Capacitors with Simultaneously Giant Energy Density and Efficiency Using Nanodomain Engineered BiFeO3‐BaTiO3‐NaNbO3 Lead‐Free Bulk Ferroelectrics

Abstract 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 BiFeO 3 ‐BaTiO 3 ‐NaNbO 3 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 W rec ≈8.12 J cm −3 , high efficiency η ≈90% and excellent thermal stability (±10%, −50 to 250 °C) and ultrafast discharge rate ( t 0.9 < 100 ns). Significantly enhanced dielectric breakdown strength of BiFeO 3 ‐based solid solutions is mainly attributed to the substitution of NaNbO 3 , 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.