Chemical nature of the enhanced energy storage in A-site defect engineered Bi0.5Na0.5TiO3-based relaxor ferroelectrics

Defect engineering has attracted significant interest in perovskite oxides because it can be applied to optimize the content of intrinsic oxygen vacancies (VO) for improving their recoverable energy-storage density (Wrec). Herein, we design 0.84Bi0.5+xNa0.5-xTiO3-0.16KNbO3 (−0.02 ≤ x ≤ 0.08) relaxor ferroelectric ceramics with A-site defects and discuss the influence of VO on Wrec. The composition with x = 0.02 has a high Wrec (3.35 J/cm3) as well as a high efficiency (η = 91%) at 240 kV/cm, and exhibits excellent temperature, frequency, and fatigue stabilities. This optimized composition also provides a large discharge-energy-density (WD = 1.0 J/cm3), a high power-density (PD = 66 MW/cm3), a fast discharge-rate (122 ns) at 150 kV/cm, and favorable temperature-induced charge-discharge properties (CDPs). Electron paramagnetic resonance, X-ray photoelectron, and Raman spectroscopic results reveal that the outstanding comprehensive performance of the designed materials is attributed to the coupling effect of low contents of dimeric TiTi′−VO•× clusters and high contents of trimeric TiTi′−VO••−TiTi′× clusters. This work provides key insights relevant for developing lead-free ceramics with excellent energy-storage properties (ESPs).