Polymorphic Heterogeneous Polar Structure Enabled Superior Capacitive Energy Storage in Lead‐Free Relaxor Ferroelectrics at Low Electric Field

Abstract

High‐performance energy storage dielectrics capable of low/moderate field operation are vital in advanced electrical and electronic systems. However, in contrast to achievements in enhancing recoverable energy density (Wrec), the active realization of superior Wrec and energy efficiency (η) with giant energy‐storage coefficient (Wrec/E) in low/moderate electric field (E) regions is much more challenging for dielectric materials. Herein, lead‐free relaxor ferroelectrics are reported with giant Wrec/E designed with polymorphic heterogeneous polar structure. Following the guidance of Landau phenomenological theory and rational composition construction, the conceived (Bi0.5Na0.5)TiO3‐based ternary solid solution that delivers giant Wrec/E of ≈0.0168 µC cm−2, high Wrec of ≈4.71 J cm−3 and high η of ≈93% under low E of 280 kV cm−1, accompanied by great stabilities against temperature/frequency/cycling number and excellent charging–discharging properties, which is ahead of most currently reported lead‐free energy storage bulk ceramics measured at same E range. Atomistic observations reveal that the correlated coexisting local rhombohedral‐tetragonal polar nanoregions embedded in the cubic matrix are constructed, which enables high polarization, minimized hysteresis, and significantly delayed polarization saturation concurrently, endowing giant Wrec/E along with high Wrec and η. These findings advance the superiority and feasibility of polymorphic nanodomains in designing highly efficient capacitors for low/moderate field‐region practical applications.