Temperature‐Mediated Defect Engineering in Cu _2‐x S for Tailoring Dielectric Response Properties

ABSTRACT Defect engineering is an effective strategy for tuning the electromagnetic properties of materials to enhance microwave absorption performance. However, the mechanism of the materials by which variations in intrinsic defect type and concentration govern the dielectric behavior has not been fully elucidated. Herein, single‐phase Cu 2‐x S with controllable defect states is successfully synthesized via a facile solvothermal method. A te–mperature‐driven defect evolution strategy is employed to systematically investigate the influence of intrinsic defect concentration and distribution on the dielectric properties. It is shown that the concentration of copper vacancies exhibits an increasing and then decreasing trend, while the density of dislocations show a consistent rise with temperatur, which significantly affect the ε values of Cu 2‐x S. The sample synthesized at 170°C exhibits an optimal synergistic distribution of high‐concentration copper vacancies and dislocations, which effectively improves impedance matching and significantly enhances dielectric loss. Consequently, it demonstrates outstanding electromagnetic wave absorption performance, achieving a minimum reflection loss (RL min ) of ‐51.85 dB and an effective absorption bandwidth (EAB) of 4.95 GHz (13.05–18 GHz) at a thickness of 1.7 mm, covering 82.5% in the entire Ku‐band. The proposed temperature‐driven defect engineering strategy establishes a definitive defect structure and dielectric performance relationship in Cu 2‐x S.