External Electric Field‐Assisted TS Vacancy Mediation for Accelerating Dipole Polarization to Enhance Electromagnetic Attenuation

Abstract Defect engineering has been widely employed in the design of electromagnetic wave (EMW) absorbing materials by tuning defect types, concentrations, and distributions. Building on these advances, external electric field (EEF) modulation has drawn considerable attention as an emerging strategy, distinguished by its non‐contact and dynamic regulation of defect formation. Nevertheless, how to actively guide vacancy formation during synthesis using EEF remains an urgent challenge. Here, an EEF‐assisted synthesis strategy that enables the active reconstruction of electronic structures and defect states in Ternary sulfides (TS) is reported. Specifically, the applied EEF lowers the migration barrier of cations (Cu 2 ⁺, Co 2 ⁺) and partially mobilizes S 2 − , generating vacancies that induce lattice distortion and redistribute electronic states, thereby enhancing electromagnetic response. When the applied EEF is kept below the critical threshold, it facilitates the cooperative formation of cation and anion vacancies, thereby enhancing charge separation and generating abundant dipole centers. Conversely, once the voltage surpasses this threshold, excessive field energy leads to an increase in defect density, which disrupts local structural order and ultimately weakens polarization. Using CuCo 2 S 4 (CCS) as a model system, the optimized CCS(6,7) achieves an effective absorption bandwidth of 6.51 GHz at a thickness of 1.81 mm under 7 V. Moreover, this strategy shows good generality across various TS systems (NCS, FCS, and MCS). Overall, this work reveals the vacancy‐driven dielectric response under EEF modulation and provides a controllable route to tailor defect structures for high performance TS based EMW absorbers.