Multiscale Domain and Defect Engineering for High-Performance Energy Storage in Bi(Zn _2/3 Nb _1/3 )O ₃ -Modified Ba _0.85 Ca _0.15 Zr _0.1 Ti _0.9 O ₃ Relaxor Ferroelectrics

Driven by the increasing demands for miniaturization and environmental sustainability, the development of high-performance lead-free energy storage materials for electronic systems has become a pivotal research focus. However, the issues of low energy density and low breakdown strength, coupled with high leakage conductance and inadequate thermostability, are still the main obstacles facing the practical application of dielectric energy storage. Here, a synergistic strategy is proposed to optimize the energy storage performance of lead-free polycrystalline ceramics through modulating normal ferroelectrics and relaxor ferroelectrics. The high-quality Bi(Zn 2/3 Nb 1/3 )O 3 -modified Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 [(1- x )BCZT- x BZN] ceramics are designed to investigate their multiscale domain structure, relaxation behavior, defect chemistry, and energy storage properties. This approach effectively regulates the phase structure and refines the grain size, essentially breaking the long-range ordering and constructing polar nanoregions. It significantly enhances the recoverable energy density, with improvements in the maximum polarization ( P max ) and breakdown field strength ( E b ) simultaneously. The optimized composition of 0.95BCZT-0.05BZN exhibits a high recoverable energy density ( W rec ) of 2.956 J/cm 3, high storage efficiency (η) of 78.69%, and an ultrafast discharge time ( t 0.9 ) of only 68.4 ns, along with excellent fatigue endurance and remarkable frequency stability. Thermally stimulated depolarizing currents (TSDC) reveal the equilibrium of the defect chemistry in the (1- x )BCZT- x BZN dielectrics. The introduction of A-site Bi 3+ undergoes donor doping, consuming oxygen vacancies, thereby reducing leakage conductivity and increasing the breakdown electric field. Concurrently, B-site (Zn 2/3 Nb 1/3 ) 3+ composite ions enhance the relaxation properties and synergistically improve the energy storage performance.