Engineering Local Polar Frustration in Lead‐Free Dielectric Ceramics for Ultrahigh Normalized Energy Storage Performance

Lead‐free dielectric capacitors require high‐recoverable energy density and thermal stability under low operating fields to prevent premature breakdown. Here, we demonstrate a design strategy for high‐performance lead‐free dielectrics based on two key principles: selecting a highly polarizable ferroelectric matrix and engineering local polar frustration to suppress long‐range order and stabilize an ergodic relaxer state. Using the (0.94Na 0.5 Bi 0.5 TiO 3 ‐0.06BaTiO 3 )–x(0.85NaNbO 3 ‐0.15CaTiO 3 ) (NBT‐BT‐NN‐CT) as an exemplar in this work, structural analyses reveal that NN‐CT incorporation induces a frustrated polar structure characterized by the nanoscale coexistence of rhombohedral, tetragonal, and cubic‐polymorphs. Density functional theory confirms that energetic degeneracy physically prevents the formation of stable macro‐domains. The optimal composition yields wide temperature stability (±15% permittivity up to 370°C), far exceeding the X7R industrial standard, delivering a recoverable energy density of >5 J cm −3 under low field (250 kV cm −1 ) achieving an ultrahigh normalized energy density (W a ) of >0.020 mC cm −2 , 60% improvement over conventional NBT‐based counterparts in the literature (e.g., 0.012–0.015 mC cm −2 ). Furthermore, in situ synchrotron X‐ray diffraction (<160 kV cm −1 ) provides strong crystallographic evidence of this dynamic structural stability, confirming the absence of irreversible field‐induced phase transitions. These results establish polar frustration engineering as a transferable design principle for resilient, high‐performance lead‐free dielectrics.