Achieving Remarkable Amplification of Energy-Storage Density in Two-Step Sintered NaNbO₃–SrTiO₃ Antiferroelectric Capacitors through Dual Adjustment of Local Heterogeneity and Grain Scale

Abstract

Antiferroelectric (AFE) materials exhibit outstanding advantages against linear or ferroelectric (FE) dielectrics in high-performance energy-storage capacitors. However, their energy-storage performances are usually restricted by both extremely large hysteresis and insufficiently high driving field of the AFE-FE phase transition, which has been a longstanding issue to be overcome in the community. In this work, we report a two-step sintered 0.83NaNbO₃-0.17SrTiO₃ (NN-ST) lead-free relaxor AFE R-phase ceramic with high relative density of ≥95% and large spans of average grain sizes from 1.2 to 8.2 μm, strikingly achieving a giant amplification of recoverable energy-storage density (<i>W</i>_rec) by 176%. Analyses of permittivity-temperature curves, Raman spectrum and microstructure demonstrate that remarkably enhanced <i>W</i>_rec values should be ascribed to the dual adjustment of local heterogeneity (nanoscale) and grain scale (microscale), resulting in the enhanced threshold field strength for dielectric breakdown and the increased critical electric fields for the AFE-FE phase transition. A high <i>W</i>_rec ≈ 1.60 J/cm³, a fast discharging rate <i>t</i>_0.9 ≈ 520 ns, large current density ∼788 A/cm², and large power density ∼55 MW/cm³ are achieved at room temperature in the NN-ST ceramic sample with an average grain size of ∼1.2 μm. These results suggest that the multiscale structure regulation should be an efficient way for achieving enhanced energy-storage properties in NN-ST relaxor AFE ceramics through a two-step sintering technique.