Enhanced energy storage density of Sr0.7BixTiO3 lead-free relaxor ceramics via A-site defect and grain size tuning

[Display omitted] •Moderate Bi3+ content is helpful to enhance activation energy and breakdown field.•Through introducing A-site defect, the slim loop and high ΔP are received in SBT2.•Ultrahigh Wrec of 4.77 J/cm3and η of 85.7% were obtained in Sr0.7Bi0.2TiO3 ceramic.•Sr0.7Bi0.2TiO3 ceramic shows good temperature stability at 20–160 °C.•An outstanding fatigue resistance after 105 cycles was achieved in Sr0.7Bi0.2TiO3. The application of dielectric capacitors with high energy density is very important to solve the increasingly serious energy crisis. However, the further improvement of energy density is seriously confining by their poor breakdown fields. In this work, outstanding energy storage performance is achieved in Sr0.7BixTiO3 (x = 0.1, 0.2, 0.3 and 0.4) ceramics via A-site defect and grain size tuning. It was found that the moderate Bi3+ content is helpful to reduce sintering temperature and refine grain size, which lead to higher activation energy and breakdown field. Besides, moderate Bi3+ doping in A-site enhances polarity owing to the hybridizations between 6p orbital of Bi and 2p orbital of O. Thus, a high recoverable energy density of 4.77 J/cm3 with prominent efficiency of 85.7% at 570 kV/cm is realized in Sr0.7Bi0.2TiO3 ceramic. Moreover, the Sr0.7Bi0.2TiO3 ceramic also displays superior thermal stability from 20 °C to 160 °C and excellent fatigue endurance over 105 cycles. Our results in this work offer a better understanding and design methodology for developing novel high-performance dielectric capacitors.