Excellent energy storage capability in Sr0.6Ba0.4Nb2O6-based ceramics via incommensurate modulation and grain boundary reinforcement

The energy storage performances for tungsten bronze ferroelectric ceramics have always been constrained by the weak relaxor behavior and low breakdown strength. To enhance the energy storage capacity of the tungsten bronze ferroelectric ceramics, a synergistic two-step optimization strategy is proposed based on the Sr0.6Ba0.4Nb2O6 ceramic in this work, that is, enhance the relaxor behavior to generate slim hysteresis loops through the introduction of Bi0.5K0.5TiO3, and then optimize the microstructure to improve the breakdown strength by adding the sintering aid CuO. Ultimately, a remarkable comprehensive performance is achieved, characterized by a recoverable energy storage density of approximately 6.31 J/cm³ and an efficiency of about 91.8 % under 600 kV/cm. Notably, a high power density (∼178 MW/cm³) and an ultrafast discharge speed (<65 ns) are simultaneously attained, indicating excellent capacitive performance. Moreover, it is revealed that the enhanced relaxor behavior is closely related to the incommensurate modulation structure in the ceramic, while the improved breakdown strength should be ascribed to the reinforced grain boundary, which collectively contribute to the superior energy storage performances.