Synergistic enhanced energy storage performance of NBT-KBT ceramics by K_0.5Na_0.5NbO₃ composition design

(1–x)(0.8Na_0.5Bi_0.5TiO₃-0.2K_0.5Bi_0.5TiO₃)-xK_0.5Na_0.5NbO₃ (x = 0, 0.1, 0.2, 0.3, 0.4) (NBT-KBT-KNN) ceramic solid solution was synthesized by solid phase method through designing KNN composition. XRD, Raman and SEM results show that NBT-KBT-KNN ceramics form solid solutions with a stable perovskite structure. The dielectric temperature spectrum and impedance spectrum analysis confirmed that the relaxor ferroelectrics (RFE) properties enhanced with increasing KNN content. The piezoresponse force microscopy (PFM) results reveal that the introduced KNN disrupts the microdomains of NBT-KBT ceramics and promotes the formation of nanodomains, leading to enhanced energy storage properties. The breakdown electric field strength (BDS) was also increased with increasing KNN content, and maximum value was obtained at x = 0.2. The addition of KNN can obviously improve energy storage performance (ESP). At 255 kV cm^–1, x = 0.2 produced excellent ESP with recoverable energy storage density (W_rec), amazingly normalized response (ξ), efficiency (η) and maximum polarization (P_max) are 3.38 J cm^–3, 132.55 J kV^–1 m^–2, 85.4 %, and 45.76 μC cm^–2, respectively. ESP is also stable in terms of frequency and temperature at (1–100 Hz) and (20–140 °C). At 120 kV cm^–1, the discharge energy density (W_dis), power density (P_D), Current density (C_D) and time for releasing 90 % of total energy density (t_0.9), are 0.202 J cm^–3, 23.43 MW cm^–3, 390.42 A cm^–2, and 56.6 ns. These findings demonstrate that NBT-KBT-KNN ceramics have the ability to be reliable energy storage and pulse power capacitors.