Temperature dependence of negative permittivity behavior in graphene/alumina ceramic metacomposites

Herein, graphene/alumina (GR/Al2O3) ceramic metacomposites with negative permittivity were prepared by hot press sintering to investigate the inherent connection between negative permittivity and external temperature. An electrical percolation phenomenon was observed in the composites with the increasing GR content. The permittivity changed from positive to negative, which was motivated from the formation of continuous three-dimensional GR networks in the composites. The negative permittivity was attributable to low-frequency plasma state of the freed electrons in the GR networks. In addition, the negative permittivity behavior was temperature-dependent in the composites with high GR contents. The higher external temperatures led to the larger absolute values of negative permittivity, and yet the negative permittivity varied very little by applying various temperature, compared to changing the additive amount of GR. As the external temperature elevated, the variation amplitude of negative permittivity enlarged in the composites with higher GR contents.