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

Lead-free antiferroelectric (AFE) ceramics have attracted increasing attention in recent years 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(Mg0.5Ti0.5)O3 (NN-BMT) perovskite solid solutions were reported to obviously exhibit AFE phase structure dependent energy-storage performances, evolving from Wrec ~1.08 J/cm3 and η ~19% at x=0.05 with orthorhombic P phase (Pbma) under 25 kV/mm to 3.12 J/cm3 and 74%, respectively, at x=0.08 with orthorhombic R phase (Pnma) under 30 kV/mm 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. Particularly, the MnO2 doped 0.92NN-0.08BMT sample exhibits giant Wrec ~5.57 J/cm3 and high η ~71% as well as excellent charge-discharge performance (CD=636.7 A/cm2, PD=63.7 MW/cm3 and t0.9 ~85 ns), as well understood by means of the detailed analysis of the grains 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.