A/B‐site co‐doping strategy driven two‐phase proportional equilibrium to optimize energy storage property in Bi0.5Na0.5TiO₃

Lead‐free perovskite ceramics have emerged as promising candidates for energy storage applications due to their excellent dielectric properties and environmental compatibility. Among them, Bi 0.5 Na 0.5 TiO 3 (BNT)‐based ceramics stand out for large spontaneous polarization ( P S ) and high Curie temperature ( T C ). However, practical applications of BNT are hindered by challenges such as high dielectric loss and low breakdown electric field strength, which limit their energy storage capabilities. To address the limitations, this work proposes a second component solid solution and dual‐site doping strategy with Ca 2+ substitution at the A‐site and Hf 4+ substitution at the B‐site, then the 0.65(Bi 0.5 Na 0.5 ) 1‐ x Ca x Hf y Ti 1‐ y O 3 ‐0.35Sr 0.7 Bi 0.2 TiO 3 (BNC x H y T‐SBT, x, y = 0, 0.03, 0.05, 0.07, 0.09) ceramics were designed and synthesized. At the optimized composition ( x, y = 0.07), BNC 0.07 H 0.07 T‐SBT ceramic exhibits a recoverable energy density of 3.45 J/cm 3 under 250 kV/cm electric field, representing more than 30% enhancement in recoverable energy density compared to the undoped BNT–SBT, with an energy efficiency of 83%. Multi‐level microstructure characterization and analysis indicates that Ca 2+ /Hf 4+ co‐doping stabilizes the TiO 6 octahedral structure, refines grain size and promotes nano‐domains formation. In addition, BNC 0.07 H 0.07 T‐SBT ceramic achieves a balanced coexistence of P 4bm and R 3c phases, significantly enhancing polarization dynamics and relaxor behavior, thereby maximizing energy storage performance. This work provides critical insights into phase engineering and offers a viable strategy for developing high‐performance energy storage ceramics.