Excellent energy-storage performance in BNT-BT lead-free ceramics through optimized electromechanical breakdown

Dielectric capacitors with high recoverable energy storage density (W_rec) are in urgent demand for clean energy technologies. However, their lower breakdown strength (E_b) strongly limits their energy storage performance. We, herein, propose a facile method to enhance E_b by enhancing mechanical strength via second phase modulation. The efficiency of this method is validated in the (1-x)(0.94Na_0.5Bi_0.5TiO₃-0.06BaTiO₃)-xSr(Ta_0.5Sb_0.5)O₃ ((BNT-BT)-xSTS, x = 0.1, 0.15, 0.2, 0.25, and 0.3) ceramics. The introduction of Sr(Ta_0.5Sb_0.5)O₃ (STS) increases the relaxor degree, refines grain size, and most importantly, creates a second phase of BiSb₂O₇, which hinders dislocation movement and improves mechanical strength. Our results show that the breakdown strength strongly depends on the mechanical strength. The highest hardness of 7.42 GPa accompanied by the largest E_b of 620 kV/cm was obtained in (BNT-BT)-0.25STS sample. The sample exhibits the best energy storage properties of a large W_rec = 8.3 J/cm³, a high efficiency of 82.3 %, and excellent temperature/frequency stability. Furthermore, the sample also exhibits good charge/discharge stability and ultra-fast transient discharge time (62.26 ns). This work provides a theoretical guidance for developing lead-free dielectrics with superior energy-storage performance.