Dual‐Phase Design Enables High Capacitive Energy‐Storage Capacity Under Moderate Electric Fields in Relaxor Ferroelectric Ceramics

ABSTRACT Advanced electronic systems rely heavily on the development of high‐performance dielectric ceramic capacitors. However, achieving simultaneous improvements in both recoverable energy density ( W _rec ) and efficiency ( η ) under moderate electric fields remains a significant challenge for practical applications. In this study, we engineer a dual‐phase perovskite structure in (Bi _0.5 Na _0.5 )TiO ₃ ‐based ceramics through an in situ phase separation to address this issue. The resulting grain‐separated dual‐phase ceramics exhibit two interacting relaxor phases with distinct nanoscale polar structures and heterogeneous stress, resulting in large polarization, low polarization hysteresis, and delayed polarization saturation. Additionally, a relatively high breakdown strength is achieved through an increased bandgap, reduced oxygen vacancy concentration, and enhanced electrical homogeneity, complemented by the dual‐phase structure, which increases the length and the meandering of the electrical‐tree propagation path. As a result, the optimized dual‐phase ceramic exhibits exceptional overall performance, with a high energy‐storage coefficient of 0.014 µC/cm ² accompanied by a large W _rec of 5.84 J/cm ³ and an ultrahigh η of 92% under 420 kV/cm, along with excellent stability, and robust charge–discharge characteristics. This study presents a practical strategy for designing high‐performance dielectric energy‐storage ceramics that operate under moderate electric fields, providing valuable insights for tailoring functional properties in ferroelectrics.