Pb/Bi-free Tungsten Bronze-Based Relaxor Ferroelectric Ceramics with Remarkable Energy Storage Performance

In this study, a Pb/Bi-free Sr2KNb5O15-based tungsten bronze relaxor ceramic system was developed for possible energy storage applications via the site engineering technology. The introduction of Ta at the Nb site enhanced the breakdown strength and relaxor nature of the Sr2KNb5O15 ceramic. An extremely high energy storage density (∼3.84 J/cm3) accompanied by a remarkable energy storage efficiency (∼93.2%) was obtained under an applied electric field of 410 kV/cm in the composition of Sr2KNb4.2Ta0.8O15. Meanwhile, the ceramic exhibited a relatively wide frequency stability (1–500 Hz) and thermal stability (30–120 °C) and displayed a remarkable fatigue endurance after 104 cycles. Even more surprisingly, the Sr2KNb4.2Ta0.8O15 ceramic processed excellent discharging performances with a short discharge time (τ0.9 < 75 ns), a large discharge current density (1019 A/cm2), and an amazing power density (125.6 MW/cm3). The impressive performances demonstrated that the Sr2KNb4.2Ta0.8O15 tungsten bronze ceramic might be a potential Pb/Bi-free dielectric material for high-power pulse capacitor applications.