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

The ε-negative property in metacomposites has triggered tremendous interest in electromagnetic fields. In this work, a tunable and weakly ε-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 ε-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 ε-negative property was explained by superposition of the Drude model and Lorentz model. It is noteworthy that the weakly ε-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 ε-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 ε-negative property, as clarified by equivalent circuit models. This work presents a novel design paradigm of ternary metacomposites with a tunable and weakly ε-negative property, which will greatly facilitate its practical applications in electromagnetic shielding, high-permittivity capacitors, and metamaterials.