Large energy-storage density in transition-metal oxide modified NaNbO3–Bi(Mg0.5Ti0.5)O3 lead-free ceramics through regulating the antiferroelectric phase structure

Abstract

Lead-free antiferroelectric (AFE) ceramics have attracted increasing attention in recent years for application in high-power capacitors owing to both environmental friendliness and high energy density. However, the relevant research progress has been seriously restricted by the limited amount of AFE candidate materials with low cost and excellent properties, which significantly rely on the AFE phase stability and crystal symmetry. In this work, NaNbO₃–Bi(Mg_0.5Ti_0.5)O₃ (NN–BMT) perovskite solid solutions were reported to obviously exhibit AFE phase structure dependent energy-storage performances, evolving from W_rec ∼ 1.08 J cm⁻³ and η ∼ 19% at x = 0.05 with an orthorhombic P phase (Pbam) under 25 kV mm⁻¹ to 3.12 J cm⁻³ and 74%, respectively, at x = 0.08 with an orthorhombic R phase (Pnma) under 30 kV mm⁻¹ owing to the transition of square-like double hysteresis loops into slim and double-like ones and the increased testable electric fields. Most interestingly, doping 0.5 mol% transition-metal oxides (CuO, CeO₂ and MnO₂) was found to evidently improve the sintering behaviour, bulk resistivity and defect structure, thus leading to largely enhanced dielectric breakdown strength. In particular, the MnO₂ doped 0.92NN–0.08BMT sample exhibits a large W_rec of ∼ 5.57 J cm⁻³ and a high η of ∼ 71% as well as excellent charge–discharge performance (C_D = 636.7 A cm⁻², P_D = 63.7 MW cm⁻³ and t_0.9 ∼ 85 ns), determined by means of the detailed analysis of the grain size distribution, impedance and X-ray photoelectron spectra. The results demonstrate that NN–BMT bulk ceramics could be very competitive lead-free AFE materials for energy-storage capacitors in pulsed power devices.