Ultrahigh Permittivity of Surface-State-Dominated Bi₂Te₃ Nanosheets for Low-Frequency Microwave Absorption

Low-frequency microwave absorption poses an important challenge due to the excessive thickness of absorbers, which inherently correlates with wavelength. Herein, Bi₂Te₃ nanosheets were synthesized via a solvothermal method to achieve high permittivity, aiming to address the issue of low-frequency microwave absorption. The as-prepared nanosheets demonstrate a tunable ultra-high permittivity (up to 282) at 2 GHz, accompanied by a loss tangent below 0.81 and pronounced frequency dispersion characteristics. The nanosheet material demonstrates a synergistic balance of ultrahigh permittivity and appropriate dielectric loss, attributed to its surface-state-conducting and bulk-insulating character. At 2.4 GHz, the composite material composed of Bi₂Te₃ nanosheet achieves an effective absorption with an electrical thickness of 0.032, which is significantly thinner than those reported for state-of-the-art microwave absorbing materials. By leveraging the high permittivity and pronounced frequency dispersion characteristics of Bi₂Te₃ nanosheet composites, broadband microwave absorption is achieved across both 2- to 6-GHz and 6- to 18-GHz ranges through multilayered architectures. This work provides a strategic approach to overcome the longstanding challenge of broadband low-frequency microwave absorption.