Ultrahigh Energy Storage in Tungsten Bronze Dielectric Ceramics Through a Weakly Coupled Relaxor Design

Dielectric energy-storage capacitors, known for their ultrafast discharge time and high-power density, find widespread applications in high-power pulse devices. However, ceramics featuring a tetragonal tungsten bronze structure (TTBs) have received limited attention due to their lower energy-storage capacity compared to perovskite counterparts. Herein, a TTBs relaxor ferroelectric ceramic based on the Gd_0.03 Ba_0.47 Sr_{0.485-1.5 x} Sm_x Nb₂ O₆ composition, exhibiting an ultrahigh recoverable energy density of 9 J cm^-3 and an efficiency of 84% under an electric field of 660 kV cm^-1 is reported. Notably, the energy storage performance of this ceramic shows remarkable stability against frequency, temperature, and cycling electric field. The introduction of Sm³⁺ doping is found to create weakly coupled polar nanoregions in the Gd_0.03 Ba_0.47 Sr_0.485 Nb₂ O₆ ceramic. Structural characterizations reveal that the incommensurability parameter increases with higher Sm³⁺ content, indicative of a highly disordered A-site structure. Simultaneously, the breakdown strength is also enhanced by raising the conduction activation energy, widening the bandgap, and reducing the electric field-induced strain. This work presents a significant improvement on the energy storage capabilities of TTBs-based capacitors, expanding the material choice for high-power pulse device applications.