Significant advancements in energy density of NN-based anti-ferroelectric material: A breakthrough in low electric field region design strategies

• Coexistence of orthorhombic Pbma and Pnma phases are observed in optimized ceramic. • A giant energy-storage coefficient (W rec /E = 0.022μC/cm 2 ) developed at low fields. • Stable temperature, frequency, and fatigue cycles are obtained in 0.92NN-0.08BSmF. • Introduction of dynamic PNRs to enhance relaxor properties has also been proved. High-performance perovskite dielectric ceramics exhibiting outstanding energy storage densities at low electric field regions are crucial for advancing miniaturized and integrated capacitors, overcoming the limitations imposed by high electric fields. Achieving superior recoverable energy density ( W rec ) and energy efficiency ( η ) with a high energy-storage coefficient ( W rec /E ) at low fields remains a significant challenge in dielectric energy storage research. In this regard, we have reported giant W rec /E and relaxor anti-ferroelectric properties via a combinational optimization of lead-free (1-x)NaNbO 3 –xBi 0.9 Sm 0.1 FeO 3 (0 ≤ x ≤ 0.10) {abbreviated as (1-x)NN-xBSmF} solid solutions . BSmF incorporation results in high polarization strength , the coexistence of orthorhombic P and R phases (indicating Pbma and Pnma space group, respectively), anti-parallel polar nano regions ( PNRs ), refined grain sizes, large band-gap energy, and most importantly, suppressed interfacial polarization. Consequently, optimized 0.92NN-0.08BSmF ceramic exhibits ultrahigh W rec /E of ∼0.022 μC/cm 2 with high W rec of ∼4.1 J/cm 3 and high η of ∼82 % under a low electric field of ∼190 kV/cm, surpassing most recently published energy-storage bulk ceramics. A superior temperature (∼ up to 140 °C), frequency (∼ up to 180 Hz), and fatigue (∼ up to 10 5 ) stability at 128 kV/cm have also been observed in the optimized ceramic. The above results indicate that this anti-ferroelectric NN-based ceramic is a promising candidate for high-energy storage at low electric field applications.