Stepwise synergistic engineering of phase and domain for excellent energy storage in AgNbO3-based ceramics

AgNbO3-based ceramics are promising lead-free candidates for pulsed-power capacitors, yet their application is hindered by high remanent polarization and large hysteresis. To address this issue, a stepwise synergistic strategy was developed through progressive substitution with Tb3+ and Ta5+ and the addition of MnO2, aiming to tailor phase stability, domain structure, and microstructure. The substitution with Tb3+ (A-site) and Ta5+ (B-site) reduced the tolerance factor and cation polarizability of AgNbO3, stabilizing the antiferroelectric (AFE) phase, suppressing octahedral tilting, and inducing highly dynamic AFE nano-domains. Subsequently, the sintering aid MnO2 was incorporated, which not only reduced defect concentration and refined grain size but also induced pronounced relaxor behavior, facilitating the formation of polar nanoregions, as evidenced by Moiré fringes. This resulted in macroscopically minimized polarization hysteresis and enhanced breakdown strength. Consequently, the 0.10 wt. % MnO2-doped Ag0.97Tb0.01Nb0.8Ta0.2O3 ceramics achieved a high recoverable energy density of 7.02 J/cm3 with an efficiency of 71.59%, demonstrating significant performance merits compared with previous reports. This work demonstrates that stepwise synergy, progressing from independent parameter control to integrated multiscale engineering, provides an effective pathway to simultaneously improve the energy storage density and efficiency in lead-free AFE capacitors.