A high energy storage density and large efficiency, together with excellent charge–discharge performance, can be simultaneously achieved in the designed tungsten bronze-structured ceramics.

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The development of lead-free ceramics with appropriate energy storage properties is essential for the successful practical application of advanced electronic devices. In this study, a site engineering strategy was proposed to concurrently decrease grain size, increase the band-gap, and enhance the relaxor nature in Ta-doped tungsten bronze ceramics (Sr2NaNb5–x Ta x O15) for the improvement of the dielectric breakdown strength and the polarization difference. As a result, the ceramic with x = 1.5, that is, Sr2NaNb3.5Ta1.5O15, exhibited superior energy density (∼3.99 J/cm3) and outstanding energy efficiency (∼91.7%) (@380 kV/cm) as well as good thermal stability and remarkable fatigue endurance. In addition, the ceramic demonstrated an ultrashort discharge time (τ0.9 < 57 ns), a high discharge current density (925.8 A/cm2) along with a high power density (78.7 MW/cm3). The energy storage properties in combination with good stability achieved in this work indicate the powerful potential of Sr2NaNb5–x Ta x O15 tungsten bronze ceramics for high-performance capacitor applications. This material can be considered as a complement to the widely studied perovskite-based relaxor ceramics and should be further investigated in the future.

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.

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