Enhancing energy storage performance in Na_0.5Bi_0.5TiO₃-based lead-free relaxor ferroelectric ceramics along a stepwise optimization route

Despite the fact that relaxor ferroelectrics (RFEs) have been extensively researched because of their various advantages, there are still barriers to simultaneously increasing their energy storage density (W_rec) and efficiency (η). By substituting Bi(Mg_0.5Sn_0.5)O₃ (BMS) and optimizing the formation process, this study follows a stepwise optimization route to achieve comprehensive exceptional energy storage performance (ESP) in Na_0.5Bi_0.5TiO₃-Sr_0.85Bi_0.1TiO₃ (NBT-SBT)-based ceramics. On the premise of constructing a Sr²⁺-Sr²⁺ ion pair at the A-site to ensure a large polarization, the introduction of Mg²⁺ and Sn⁴⁺ ions at the B-site further induces a local disordered field and promotes polar nanoregions. Following that, the viscous polymer process (VPP) used to synthesize NBT-SBT-BMS ceramics can thin the thickness, reduce defects, and boost compactness, hence improving the polarization difference (ΔP) and breakdown strength (E_b). Using the stepwise optimization route, we were able to attain a high ΔP of 64.6 μC cm⁻² and an E_b of 440 kV cm⁻¹ in 0.92(0.65NBT-0.35SBT)-0.08BMS-VPP ceramics. More crucially, an ultrahigh W_rec of 7.5 J cm⁻³ and a high η of 85% are simultaneously achieved, together with excellent temperature adaptability between 20 and 120 °C. Our superb ESP exceeds the majority of previously reported NBT-based ceramics, confirming the applicability of this stepwise optimization route to other similar high-performance dielectric ceramic designs.