Structural origin of enhanced storage energy performance and robust mechanical property in A-site disordered high-entropy ceramics

Abstract: High-entropy perovskite ferroelectric materials have attracted significant attention due to their remarkably low remnant polarizations and narrow hysteresis. Thus, these materials offer high-energy density and efficiency, making them suitable for energy storage applications. Despite significant advancements in experimental research, understanding of the properties associated with structure remains incomplete. This study aims to study the structural, electric, and mechanical performances at various scales of the high-entropy (Na_0.2Bi_0.2Ca_0.2Sr_0.2Ba_0.2)TiO₃ (NBCSB) material. The results of first-principles calculations indicated that the pseudo-intralayer distortion was obviously smaller compared to the interlayer distortion. Among the various bonds, Bi–O, Ca–O, and Na–O experienced the greatest displacement. Similarly, the hybridization between O 2p and Ti 3d states with Bi 6p states was particularly strong, affecting both the ferroelectric polarization and relaxor behavior. The NBCSB materials produced using a typical solid-state process demonstrated exceptional performance in energy storage with a recoverable density of 1.53 J·cm⁻³ and a high efficiency of 89% when subjected to a small electric field of 120 kV·cm⁻¹. In addition, these ceramics displayed a remarkable hardness of around 7.23 GPa. NBCSB ceramics exhibited exceptional relaxation characteristics with minimal hysteresis and low remanent polarization due to its nanoscale high dynamic polarization configuration with diverse symmetries (rhombohedral, tetragonal, and cubic) resulting from randomly dispersed A-site ions. The excellent mechanical property is related to the dislocation-blocking effect, solid solution strengthening effect, and domain boundary effect. The findings of this study offer a comprehensive and novel perspective on A-site disordered high-entropy relaxor ferroelectric ceramics.