Realizing High Comprehensive Energy Storage and Ultrahigh Hardness in Lead-Free Ceramics

Due to the presence of pores and low density, a high recoverable energy density (W_rec) value is usually obtained at the cost of energy storage efficiency (η) in lead-free potassium sodium niobate [(K, Na)NbO₃, KNN] based ceramics, which also affects the hardness of ceramics, finally limiting the further development of practical applications. A high W_rec (∼3.60 J/cm³ ) and a high η (∼74.2%) are obtained in 0.975K_0.5Na_0.5NbO₃-0.025LaBiO₃ (0.975KNN-0.025LB) ceramics simultaneously under a high dielectric breakdown strength (DBS) of 340 kV/cm, together with a fast discharge rate (t_0.9 ∼ 46 ns) and high power density (P_D ∼ 49.4 MW/cm³). Further analysis of the intrinsic electronic structure is carried out via the first-principles calculation based on the density functional theory (DFT). An ultrahigh hardness (H) of 6.63 GPa can be accordingly obtained. This work combines excellent energy storage properties and ultrahigh hardness, which provides significant guidelines for applications in pulsed-power systems.