Relaxor regulation and improvement of energy storage properties of Sr2NaNb5O15-based tungsten bronze ceramics through B-site substitution

•A novel type of lead- and bismuth-free TTB relaxor is obtained.•The relationship between structure and electrical behavior is studied in detail.•Enhanced relaxation and high BDS are obtained based on B-site substitution.•The current ceramics show the high Wre of 2.03 J/cm3 and the η of 94%.•Excellent charging-discharging performance of Wdis of 2.22 J/cm3 and 151.1 MW/cm3 of PD are achieved. Based on B-site substitution, a series of Sr1.88La0.12NaNb4.88−xTaxTi0.12O15 tungsten bronze ceramics were prepared by traditional solid-reaction. The influence of Ta replacement on dielectric relaxor, electrical and energy storage properties has been studied in detail. The change of dielectric properties deviates from the previous crystal chemical framework, and is closely related to the structural distortion caused by the special electronic configuration of Ta. In addition, an enhanced dielectric breakdown strength was obtained, which benefited from the dense microstructure, improved insulation and widened band gap. Finally, under the combined influence of good relaxation and high dielectric breakdown strength, an energy storage density of 2.03 J/cm3 and an efficiency of 94% were achieved. More importantly, the charging-discharging performance has also been evaluated. The discharge energy density of 2.22 J/cm3 and the power density of 151.1 MW/cm3 indicate that the present ceramics are promising as high-power energy storage capacitor applications.