Relaxor antiferroelectric-relaxor ferroelectric crossover in NaNbO3-based lead-free ceramics for high-efficiency large-capacitive energy storage

Relaxor ferroic dielectrics have garnered increasing attention in the past decade as promising materials for energy storage. Among them, relaxor antiferroelectrics (AFEs) and relaxor ferroelectrics (FEs) have shown great promise in term of high energy storage density and efficiency, respectively. In this study, a unique phase transition from relaxor AFE to relaxor FE was achieved for the first time by introducing strong-ferroelectricity BaTiO3 into NaNbO3-BiFeO3 system, leading to an evolution from AFE R hierarchical nanodomains to FE polar nanoregions. A novel medium state, consisting of relaxor AFE and relaxor FE, was identified in the crossover of 0.88NaNbO3-0.07BiFeO3-0.05BaTiO3 ceramic, exhibiting a distinctive core-shell grain structure due to the composition segregation. By harnessing the advantages of high energy storage density from relaxor AFE and large efficiency from relaxor FE, the ceramic showcased excellent overall energy storage properties. It achieved a substantial recoverable energy storage density Wrec ∼ 13.1 J/cm3 and an ultrahigh efficiency η ∼ 88.9%. These remarkable values shattered the trade-off relationship typically observed in most dielectric capacitors between Wrec and η. The findings of this study provide valuable insights for the design of ceramic capacitors with enhanced performance, specifically targeting the development of next generation pulse power devices.