Compromise boosted high capacitive energy storage in lead-free (Bi0.5Na0.5)TiO3 −based relaxor ferroelectrics by phase structure modulation and defect engineering

By combining a judiciously designed phase structure and defect engineering, we have successfully achieved a BNT-based lead-free ceramic capacitor with simultaneously high energy density of 8.46 J/cm 3 and efficiency of 80.8%, concomitant with robust stability and rapid discharge, which are mainly attributed to the polymorphic R − T polar nanoregions coexistence, reduced oxygen vacancies and grain size, boosted conductivity activation energy , and enhanced electrical homogeneity. • The combination of phase structure modulation and defect engineering was proposed to enhance ESP. • High W rec (8.46J/cm 3 ), high դ (80.8 %), and ultrahigh E b (640 kV/cm) were simultaneously achieved. • Excellent stabilities and satisfactory charging-discharging performance were gained. • The structure–property correlation was explored by multiscale structure characterizations. Dielectric capacitors are vital passive components for pulsed power electronics and prioritize dielectric ceramics because of their great potential of high thermal stability and low cost in production. Nevertheless, the poor comprehensive energy storage performance (ESP) has limited their widespread development toward miniaturization, lightweight, and integration, especially via an eco-friendly lead-free approach. Herein, we adopt the compromise optimization between phase structure modulation and defect engineering to upgrade the ESP of lead-free (Bi 0.5 Na 0.5 )TiO 3 -based ceramics. The phase structure modulation regulates the ratio of rhombohedral ( R ) and tetragonal ( T ) phases and promotes the macrodomain- nanodomain transition, consequently fostering polymorphic R − T polar nanoregions coexistence. Subsequently, via defect engineering strategy, the reduction in defects (such as oxygen vacancies) and grain size, boost in conductivity activation energy, and enhancement in electrical homogeneity collectively promote high breakdown strength. This cascade effect generates impressive ESP, ultimately realizing a large recoverable energy density of 8.46 J/cm 3 and efficiency of 80.8 % under 640 kV/cm, which also shows robust stabilities against temperature/frequency/cycle and satisfactory charging-discharging performance. This work highlights that the approach of compromise optimization via phase structure modulation and defect engineering is a robust pathway for the design of high-performance lead-free dielectric ceramics.