Giant energy density with ultrahigh efficiency achieved in NaNbO3-based lead-free ceramics with polymorphic antiferrodistortive polar nanodomains

Abstract

The development of dielectric ceramics with simultaneously high energy-storage density (Wrec) and efficiency (η) for capacitive energy storage poses a significant challenge. Herein, an effective strategy to achieve ultrahigh comprehensive energy-storage performance via designing polymorphic antiferrodistortive polar nanodomains is proposed, successfully realizing a giant Wrec of ∼7.5 J/cm3 with an ultrahigh η of ∼94 % in (0.9-x)NaNbO3-0.1BaZrO3-xBi(Mg0.5Ti0.5)O3 ((0.9-x)NN-0.1BZ-xBMT) lead-free ceramics at x = 0.08. The studied ceramic also exhibits excellent temperature-insensitive charge–discharge performances of high power density ∼204 ± 3 % MW/cm3, high discharge energy density ∼3.7 ± 3 % J/cm3 and fast discharge rate < 60 ns within 25–150 °C. The observation of ex-/in-situ piezoresponse force microscopy and transmission electron microscope reveals that polar nanodomains with multiple antiferrodistortive FE symmetries and diverse scales exhibit dissimilatory transformation behavior into FE microdomains during electric field loading/unloading, being responsible for a low-hysteresis polarization-field response with a near-zero remnant polarization and a high maximum polarization. Meanwhile, optimized bandgap structure and grain morphology contribute to the enhanced ceramic resistivity and conductivity activation energy as well as suppressed leakage current, resulting in significantly improved dielectric breakdown strength. These results demonstrate a feasible strategy for developing novel high-performance dielectric ceramics for high-efficiency capacitive energy storage.