Regulating the Interphase Strain in High‐Entropy Oxide Thin Films – An Approach to Attaining Giant Energy Storage Capability under Moderate Electric Fields

Abstract In recent years, high‐entropy dielectrics have demonstrated superior performance in capacitive energy storage devices. However, the impressive energy storage density of these materials typically necessitates ultrahigh external electric fields, which restricts the range of their practical applications. In this work, an interphase strain engineering strategy is developed, i.e., through the modulation of the deposition temperatures and post‐deposition cooling rates, an appropriate amount of pyrochlore nanocolumns is introduced into high‐entropy oxide epitaxial films, exerting a nontrivial level of interphase strain on adjacent perovskite lattices. This interphase strain transforms the dispersive polar nanodomains into a compact polar slush state, enabling a delicate balance between spontaneous polarization and breakdown strength. Ultimately, the (Bi _0.5 Na _0.5 )(Ti _0.2 Sn _0.2 Hf _0.2 Fe _0.2 Nb _0.2 )O ₃ (BNTSHFN) high‐entropy oxide thin film in this work exhibits a giant recoverable energy density of 93 J cm ⁻³ and a high efficiency of 83% under a moderate electric field of 3.6 MV cm ⁻¹ . This work provides an innovative idea for designing high‐entropy capacitive energy storage devices with promising potential in real‐world scenarios.