Graphene-Carbon Black/CaCu3Ti4O12 Ternary Metacomposites toward a Tunable and Weakly ε-Negative Property at the Radio-Frequency Region

The epsilon-negative property in metacomposites has triggered tremendous interest in electromagnetic fields. In this work, a tunable and weakly epsilon-negative property was obtained in graphene-carbon black/ CaCu3Ti4O12 (GR-CB/CCTO) ternary metacomposites prepared by a low-temperature pressure-less sintering process. Interestingly, two types of the epsilon-negative mechanism, that is, induced electric dipole generated from isolating GR-CB units and low-frequency plasmonic state generated from GR-CB networks, have been observed in GR-CB/CCTO metacomposites. Hence, the epsilon-negative property was explained by superposition of the Drude model and Lorentz model. It is noteworthy that the weakly epsilon-negative value ranged from the quadratic to third order of magnitude of ten and was tuned by adjusting the content of randomly distributed GR-CB units. The epsilon-near-zero behavior was observed at around 475 and 85 MHz for the composites with GR-carbon nanotube contents of 8 and 10 wt %, respectively. In addition, ac conductivity spectra showed a change of conduction mechanism from hopping conduction to metal-like conduction with increasing GR-CB content. The inductive character derived from the GR-CB networks significantly correlates with the epsilon-negative property, as clarified by equivalent circuit models. This work presents a novel design paradigm of ternary metacomposites with a tunable and weakly epsilon-negative property, which will greatly facilitate its practical applications in electromagnetic shielding, high-permittivity capacitors, and metamaterials.