The enhanced energy storage properties of (1-x)(0.94BNT-0.06BT)-x(Bi_0.2Na_0.2K_0.2La_0.2Sr_0.2)TiO₃ solid solutions

A strategy is developed to enhance the energy storage properties of lead-free Bi_0.5Na_0.5TiO₃-based solid solutions, which is implemented through coupling the lattice instability in 0.94(Bi_0.5Na_0.5)TiO₃-0.06BaTiO₃ (0.94BNT-0.06BT) ferroelectric with a composition at its morphotropic phase boundary with the chemical disorder in (Bi_0.2Na_0.2K_0.2La_0.2Sr_0.2)TiO₃ (BNKLST) high-entropy ceramic (HEC). The addition of BNKLST in 0.94BNT-0.06BT could suppress the relaxor behaviors in the resulting solid solutions (1-x)(0.94BNT-0.06BT)-xBNKLST. With increasing content x, BNKLST may triggers more polar nano-regions which are in ergodic states at elevated temperatures. As a result, the thermal stability for energy storage properties is increased. In particular, the solid solution with x = 0.3 not only possesses large dielectric constants but also has a low content of oxygen vacancies, beneficial to its dielectric properties; It exhibits an excellent recoverable energy storage density of 2.24 J/cm³ under an electric field of 140 kV/cm, and a good thermal stability at 50 kV/cm with energy storage efficiency η >80 % up to 200 °C. The results demonstrate that the synergy effect of lattice instability and chemical disorder in the solid solutions is effective in enhancing energy storage properties of HECs, facilitating the design and optimization of dielectric energy storage devices.