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

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_0.5Na_0.5)TiO₃-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/cm² accompanied by a large W_rec of 5.84 J/cm³ 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.