Enhanced Energy Storage Performance in Na_0.5Bi_0.5TiO₃-Sr_0.7Bi_0.2TiO₃ Relaxor Ferroelectric Thin Films by Entropy Design

Dielectric thin film capacitors have attracted immense attention in modern pulsed power electronic systems as essential energy-storage components. Nevertheless, there are still a lot of challenges in realizing high recoverable energy densities and efficiencies. Herein, an effective strategy is proposed to achieve an enhanced energy storage performance by increasing atomic configuration entropy and grain refining, through incorporation of multifarious heterovalent cations in A sites. By including Sr0.7Bi0.2TiO3 (SBT) into Na0.5Bi0.5TiO3 (NBT) ferroelectric, slender polarization–electric field hysteresis loops with delayed polarization saturation are realized in the intermediate compositions. The introduction of SBT in NBT increases the heterogeneity of the multivalent cations in A-sites and the atomic configuration entropy along with the existence of atomic disorder and lattice distortion, resulting in grain refining and smaller nanodomains, which enhances the relaxation characteristics and suppresses the early polarization saturation. While further addition of SBT decreases the atomic configuration entropy and the degree of atomic disorder and lattice distortion, the sizes of grains and nanodomain increase, and thus the remnant polarization increases, leading to decreased energy density and efficiency. Finally, 0.4NBT-0.6SBT thin films obtain an enhanced recoverable energy storage density of 63 J/cm3 and an energy storage efficiency of 68%. Moreover, excellent thermal stability (from 20 to 220 °C) and strong fatigue endurance (up to 107 cycles) are achieved. These results demonstrate a heuristic strategy to design high-performance dielectric materials by increasing the atomic configuration entropy.