Excellent energy-storage performance realized in SANNS-based tungsten bronze ceramics via synergistic optimization strategy

A series of tungsten bronze (Sr_2–xBi_xAg_0.2Na_0.8) (Nb_4.8–xZr_xSb_0.2)O₁₅ compounds were fabricated by solid-state method to systematically study the impacts of co-doping Bi³⁺/Zr⁴⁺ ions in A/B-sites on the structures, relaxor characteristics, and energy-storage performances. The relationship between structures and relaxor behaviors are summarized as three main points: (1) with increasing the amount of co-doping Bi³⁺/Zr⁴⁺ ions, the crystal structure evolved from an orthorhombic Bbm2 to a tetragonal paraelectric P4/mbm symmetry at room temperature; (2) enhancing relaxor characteristics at room temperature was achieved by tailoring the temperature region of T_m−T_B (T_m is the dielectric maximum temperature, T_B is the Burns temperature), which could be attributed to the incommensurate local structure modulations associated with the orthogonal distortion of P4bm symmetry and the appearance of microdomains; (3) The co-introduction of Bi³⁺ and Zr⁴⁺ could also played an important role in inhibiting the grain sizes, increasing resistivity and band-gap to enhance the breakdown strength. Finally, a superior recoverable energy-storage density (3.61 J/cm³) and an ultrahigh energy efficiency (90%) were obtained simultaneously at 389 kV/cm in BZ_0.05 ceramics. Moreover, an outstanding power density (158.98 MW/cm³) together with a current density of 1422.29 A/cm² was realized at 220 kV/cm from the charging−discharging performance measurements. The excellent energy-storage performance (ESPs) make the environmentally friendly BZ_0.05 samples show enormous potential in high-power capacitor applications.