Enhanced energy storage density of Sr_0.7Bi_xTiO₃ lead-free relaxor ceramics via A-site defect and grain size tuning

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 Sr_0.7Bi_xTiO₃ (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 Sr_0.7Bi_0.2TiO₃ ceramic. Moreover, the Sr_0.7Bi_0.2TiO₃ 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.