Local Isomeric Polar Nanoclusters Enabled Superior Capacitive Energy Storage Under Moderate Fields in NaNbO 3 ‐Based Lead‐Free Ceramics

The high-field energy-storage performance of dielectric capacitors has been significantly improved in recent years, yet the high voltage risks of device failure and large cost of insulation technology increase the demand for high-performance dielectric capacitors at finite electric fields. Herein, a unique superparaelectric state filled with polar nanoclusters with various local symmetries for lead-free relaxor ferroelectric capacitors is subtly designed through a simple chemical modification method, successfully realizing a collaborative improvement of polarization hysteresis, maximum polarization, and polarization saturation at moderate electric fields of 20-30 kV mm^-1. Therefore, a giant recoverable energy density of ≈5.0 J cm^-3 and a high efficiency of ≈82.1% are simultaneously achieved at 30 kV mm^-1 in (0.9-x)NaNbO₃-0.1BaTiO₃-xBiFeO₃ lead-free ceramics, showing a breakthrough progress in moderate-field comprehensive energy-storage performances. Moreover, superior charge-discharge performances of high-power density ≈182 MW cm^-3, high discharge energy density ≈4.3 J cm^-3 and ultra-short discharge time <70 ns as well as excellent temperature stability demonstrate great application potentials for dielectric energy-storage capacitors in pulsed power devices. This work provides an effective and paradigmatic strategy for developing novel lead-free dielectrics with high energy-storage performance under finite electric fields.