High energy storage density and efficiency in nanostructured (Bi_0.2Na_0.2K_0.2La_0.2Sr_0.2)TiO₃ high-entropy ceramics

High-entropy ceramics (HECs) (Bi_0.2Na_0.2K_0.2La_0.2Sr_0.2)TiO₃ (BNKLST) with single-phase perovskite structure have been successfully prepared by a modified citrate acid method. In comparison to (Bi_0.5Na_0.5)TiO₃ (BNT) ceramics prepared by the same synthesis route, the BNKLST HECs exhibit dense nanostructures with grain sizes as small as 45 nm, which are suggested to be responsible for the significantly improved electric breakdown fields and reduced leakage currents in the ceramics, and they have much enhanced elastic modulus owing to the entropy-stabilized perovskite structure. The electrical and dielectric characterizations reveal that BNKLST has high electrical resistances and dielectric constants at elevated temperatures, and, in particular, a recoverable energy storage density of 0.959 J/cm³ can be achieved under an applied electric field of 180 kV/cm. Moreover, the energy storage efficiency in BNKLST can be maintained to be larger than 90% at 40–200°C. These excellent properties suggest that entropy-stabilized BNT-based ceramics are promising dielectrics for electrical energy storage applications.