Mechanism of Delayed Polarization Saturation Induced by B‐Site Zr Doping for Enhancing Energy Storage Performance in Bi 0.5 Na 0.5 TiO 3 ‐ Sr 0.7 Bi 0.2 TiO 3 Ceramics

ABSTRACT In this work, Zr 4+ ions are introduced into the B‐site of 0.67Bi 0.5 Na 0.5 TiO 3 ‐0.33Sr 0.7 Bi 0.2 TiO 3 relaxor ferroelectric ceramics, leading to a significant improvement in energy storage performance. On one hand, Zr 4+ doping suppresses grain growth, increasing the breakdown electric field from 250 to 470 kV cm −1 . On the other hand, it tailors the phase structure by reducing the fraction of the strong polar rhombohedral phase, refines polar nanoregions (PNRs) into discrete micro‐nano polar clusters with reduced size and weakened cooperative switching, and notably alters their morphology and distribution, thereby reducing the local polarization intensity. These micro‐nano polar clusters exhibit reduced switching cooperativity under an electric field, resulting in a marked delay of polarization saturation—the electric field required to achieve a comparable polarization value is increased. Finally, the recoverable energy storage density ( W rec ) and efficiency ( η ) of the 0.67Bi 0.5 Na 0.5 Ti 0.94 Zr 0.06 O 3 ‐0.33Sr 0.7 Bi 0.2 Ti 0.94 Zr 0.06 O 3 samples are significantly improved, reaching 7.2 J cm −3 and 88.1% under 470 kV cm −1 . It also exhibits stable performance from 30–160°C, with the fluctuation of W rec lower than 5%. Moreover, it possesses a high power density of 140 MW cm −3 and an ultrafast discharge time. The proposed “delayed polarization saturation” strategy offers a new route for designing high‐performance lead‐free dielectric energy storage ceramics.