Abstract
SrTiO3 (ST)-based ceramics are considered as promising candidates for energy storage applications. However, the low polarization intensity in ST-based materials limits their energy storage performance, rendering materials that usually exhibit a low recoverable energy-storage density. In the present study, we have optimized the energy storage performance of ST-based ceramics by using a combined optimization strategy of structural engineering and microstructural regulation. High performance (Sr1-x-y-2φNayBixCaφ□φ)TiO3 (abbreviated as zSNBCT, where □ represents the Sr vacancies) ceramics were thereby designed. During composition optimization, the phase state of zSNBCT was adjusted to a critical point where the relaxor ferroelectric-paraelectric phase transition occurred around room temperature. It thus induced a strong relaxation behavior with the formation of ferroelectric polar nano-regions, yielding a high recoverable energy-storage density (Wrec) of ∼6 J/cm3 and a high energy-storage efficiency (η) of ∼92% under a large breakdown electric field of 440 kV/cm, for z = 0.2 sample. Moreover, the breakdown strength (BDS) of the 0.2SNBCT ceramic was further improved by adopting a two-step sintering and spark plasma sintering approach for the microstructural refinement. Simulation models containing grains and grain boundaries were well established using phase-field simulation and finite element analysis. These simulations came to a similar conclusion for the enhanced BDS. Namely, the fine-grained microstructure significantly hindered the growth of breakdown cracks under an applied electric field. Most importantly, the 0.2SNBCT sample showed excellent frequency stability (1−1000 Hz), thermal stability (20−140 °C), and cycling stability (105 cycles), rendering it a promising candidate for energy storage systems. Our designed strategy of structural engineering and microstructural regulation may provide a new paradigm for the design of high-performance energy storage ceramics for pulse power applications.
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