Multiple relaxor phases driving excellent energy storage performance in Na0.5Bi0.5TiO3-based ceramics via dual-site ion-pair structure design

Abstract

Dielectric ceramics have attracted extensive attention for high-power energy storage applications due to their fast charge–discharge capabilities and high power density. Bi_0.5Na_0.5TiO₃(BNT)-based lead-free ceramics are notable for their high saturation polarization and moderate breakdown electric field (E_b), but they still suffer from a low breakdown field, large hysteresis losses and insufficient efficiency. Here, we propose a strategy of dual-site ion-pair engineering by introducing Ba(Sr_0.5W_0.5)O₃ (BSW) into the BNT matrix. In this design, Ba²⁺–Ba²⁺ pairs at the A-site and Sr²⁺–W⁶⁺ pairs at the B-site induce local lattice distortion and generate strong random fields, which effectively promote the formation of multiple relaxor phases with polymorphic nanodomains. The features of electrical properties and phase-field simulations indicate that BSW doping facilitates greater compositional disorder and disruption of long-range FE order, integrating the short-range ordered antiferroelectric (AFE) nanodomains with highly disordered relaxor ferroelectric (RFE) regions to reduce the electric field-induced AFE–FE phase transition barrier. Additionally, the incorporation of BSW refines the grain size and increases microstructural homogeneity, enhancing the breakdown strength and delaying the polarization saturation. Accordingly, the 0.90BNT-0.10BSW ceramic exhibited an outstanding energy storage performance with a high W_rec of 6.57 J cm⁻³ and an η of 72% under an electric field of 450 kV cm⁻¹. In addition, the ceramic synchronously possesses an excellent transient discharge rate t_0.9 of 90 ns and a high power density P_D of 121.9 MW cm⁻³. This work suggests that dual-site ion-pair engineering is an effective approach for regulating structure–property relationships in BNT-based ceramics and provides a viable pathway for the development of high-performance lead-free dielectric materials for advanced energy storage applications.