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

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 (Bi0.5Na0.5)TiO3-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/cm3 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.