Processing conditions dependent tunable negative permittivity in reduced graphene oxide-alumina nanocomposites

In this study, reduced graphene oxide-alumina (RGO-Al2O3) metacomposites with tunable negative permittivity were obtained from spark plasma sintering method. Regulation of negative permittivity was realized by adjusting the sintering process conditions. The effects of sintering temperature and pressure on the dielectric properties of RGO-Al2O3 metacomposites were firstly studied in details. Interestingly, the Fano-like resonance phenomenon was observed in the RGO-Al2O3 metacomposites containing 8.91 and 15.01 vol% GO produced from 1000 degrees C at 50 MPa. This phenomenon was attributed to the interference of two kinds of resonances, which was different from general polarization dipole resonance. The sintering temperature regulated the permittivity via the micro-capacitance of RGO itself and the interfacial effect between RGO and Al2O3 grains. The resonance frequency was also dependent on the sintering temperature. The sintering pressure effectively controlled the value of permittivity and the resonance frequency which were influenced by the degree of GO reduction and the mutual contact between grains. With the increase of the sintering pressure, the value of permittivity increased and the resonance frequency advanced. Overall, the permittivity and the resonance frequency of the RGO-Al2O3 metacomposites were easily regulated by adjusting the sintering process conditions.