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.

A cantilever-structured magneto-mechano-electric (MME) generator comprising a magnetoelectric composite with a magnet proof mass is a potential candidate for powering autonomous wireless sensor networks. Recently, the concept of a magnetic flux concentrator (MFC) to enhance the output performance of the MME generator by focusing the ultralow-intensity magnetic field into the MME generator was introduced. However, the MFC-concentrated magnetic flux mostly focused on the end tip of the MME cantilever rather than at the magnet proof mass located on the cantilever beam. Considering that the torque generated by the magnet proof mass contributes more than half of the output power of an MME generator, optimizing the volume and position of the proof-mass with MFC is crucial for better performance. Furthermore, a smaller proof-mass is desirable for the long-term reliability of cantilever-type harvesters. Hence, we investigated the effect of the position and weight (volume) of the magnet proof mass with respect to the MFC on the output performance of the MME generator through finite element analysis and experiments. The MME generator with the lighter magnet proof mass at the optimized position generated a maximum power of 5.35 mW under a 10 Oe magnetic field, which was 210% of that of the MME configuration used in our previous study. Furthermore, the MME generator showed broadband characteristics around the practical frequency of 60 Hz, which could provide more freedom to design the harvester with high performance.