Spark plasma sintered GR-CNT/CaCu3Ti4O12 ceramic nanocomposites with tunable epsilon-negative and epsilon-near-zero property

Abstract

Graphene-carbon nanotube/copper calcium titanate (GR-CNT/CCTO) ceramic nanocomposites were prepared by spark plasma sintering (SPS) technology. The correlation between GR-CNT content and epsilon-negative property was clarified in detail. Electrical percolation behavior was confirmed in nanocomposites with GR-CNT content rising, corresponding to change from hopping conductivity to metal-like conductivity. When three-dimensional (3D) GR-CNT networks were constructed in CCTO ceramics, epsilon-negative property was obtained, originating from low-frequency collective plasma oscillation of delocalized electrons in formed networks. Epsilon-near-zero (ENZ) property was respectively obtained at ~360 MHz and ~255 MHz. The negative value of epsilon ranged from ~103 to ~104, and plasma frequency of the composites increased from 12.8 GHz to 34.6 GHz with GR-CNT content ranging from 10 wt% to 12 wt%, which was analyzed by Drude model. In addition, the dielectric loss behavior and impedance response also were discussed. The inductive character of epsilon-negative materials was expounded via equivalent circuit analysis. We provide an effective paradigm of carbon/ceramic nanocomposites with epsilon-negative property by constructing 3D GR-CNT networks, which facilitates the clarification of regulation mechanism of epsilon-negative materials.