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)NbO 3, 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/cm 3 ) and a high η (∼74.2%) are obtained in 0.975K 0.5 Na 0.5 NbO 3 -0.025LaBiO 3 (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/cm 3 ). 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.