Negative permittivity behavior in microwave frequency from cellulose-derived carbon nanofibers

Abstract

Carbon nanofibers (CNFs) with negative permittivity behavior in microwave frequency band were first reported, which were produced from freeze-drying and high-temperature carbonization using cellulose nanofibers as raw materials. The effect of carbonization temperature on CNFs’ AC conductivity and microstructure was studied in detail. The results showed that as the carbonization temperature increased, the fiber structure was remained and the AC conductivity increased due to the removal of oxygen-containing groups. When the carbonization temperature reached 1100 ℃ and above, the negative permittivity was observed in the microwave frequency range of 2–18 GHz. The reason was that the fiber structure was easy to lap into the continuous conductive network and the high AC conductivity was obtained. The frequency dispersions of permittivity conformed to the Lorentz model and/or the Drude model. It was found that as the temperature increased, the permittivity curve transitioned from the Lorentz model to Drude model because the movement of electrons gradually approached the state of free electrons under the Drude model. This work has provided a new way for the achievement of negative permittivity in microwave frequency based on lightweight carbon materials.