Highly tunable negative permittivity of carbon nanofiber/alumina metacomposites at different external temperatures

Abstract

Effective and precise modulation of negative permittivity behavior still deserved further research. Herewith, alumina (Al2O3) metacomposites with various carbon nanofiber (CNF) contents were fabricated using hot-press sintering, and the effects of CNF content and external temperature on the electrical properties of metacomposites were investigated. As the CNF content increased, a three-dimensional interconnected CNF network was formed in the composites, resulting in the conversion of the impedance characteristic and the conductivity mechanism. The composites with CNF content of 2 wt% exhibited negative permittivity behavior, owing to the low-frequency plasma state of free electrons in the CNF conducting networks, which could be well simulated by the Drude model. Excellent electromagnetic shielding performance was observed in the composites with high CNF contents at Ku band, and shielding effectiveness reached more than 30 dB with a reflection-dominated mechanism. Furthermore, the temperature-dependences of the electrical properties of the composites were explored. Both the negative permittivity and conductivity of the composites increased with external temperature rising, which were mainly attributed to the changes in free electron concentration and mobility. It was worth noting that the values of negative permittivity varied very little, which provided an effective method for precise regulation of negative permittivity. This work not only enriched the adjustment method of negative permittivity but also helped to expand the application field of metacomposites.