The multi-walled carbon nanotube/alumina (MWCNTs/Al2O3) nanocomposites embedded with the shortened MWCNTs were prepared by pressureless sintering. The microstructure, conductive behavior and complex permittivity spectra of the composites were investigated. It was found that MWCNTs, which were shortened to low aspect ratio by the controllable acid and ultrasonic treatment, uniformly dispersed in the Al2O3 matrix. A unique dielectric resonance-induced negative permittivity behavior was observed in the composites with high MWCNTs content. The negative magnitude of permittivity was small (~-50) in the testing frequency. The dielectric loss peaks being accompanied by dielectric resonance moved to the higher frequency with increasing MWCNTs content. Those composites underwent a capacitive-inductive transition with increasing frequency and their conductive mechanism was hopping conduction. This work is beneficial to explore the generation mechanism of negative permittivity, and will greatly facilitate the practical application of metamaterials.
Percolation-Induced Negative Permittivity in Multi-Walled Carbon Nanotube/Polyimide Metacomposites