A-/B-site engineering of AgNbO₃-based ceramics for high-efficiency relaxor antiferroelectric energy storage

Lead-free antiferroelectric (AFE) ceramics are promising candidates for next-generation pulsed power capacitors. However, their practical deployment remains limited by low recoverable energy density (W_rec), limited dielectric breakdown strength (E_b), and poor efficiency (η), particularly under moderate electric fields. To address these challenges, this study introduces a compositional design strategy that simultaneously engineers both A- and B-sites in AgNbO₃ (AN) perovskite ceramics. Specifically, 20 mol% Ta⁵⁺ is fixed at the B-site, while dual A-site substitution with Li⁺ and Nd³⁺ is implemented. This codoping approach enables a tunable transition from conventional AFE behavior to a relaxor-antiferroelectric-like (R-AFE-like) state. This evolution is driven primarily by A-site chemical disorder introduced by Li⁺/Nd³⁺ codoping, which disrupts long-range antiferroelectric ordering and facilitates the formation of nanodomains. In parallel, B-site Ta⁵⁺ substitution contributes by suppressing octahedral tilting and stabilizing the nonpolar phase. The optimized composition, (Ag_1−4xLi_xNd_x)(Nb_0.8Ta_0.2)O₃ at x = 0.03, delivers a remarkable recoverable energy density of 7.2 J/cm³ and an efficiency of 92.3% under a moderate electric field of 327 kV/cm. In addition, this composition demonstrates an excellent W_rec/E_b ratio and capacitor-grade reliability, including strong frequency and thermal stability, as well as ultrafast discharge characteristics (t_0.9 ≈ 40 ns) with a peak power density of 172 MW/cm³. Overall, this work provides a detailed structure–property–performance framework for designing high-efficiency, high-power, lead–free capacitors by harnessing tunable relaxor–antiferroelectricity.