Freeze-drying assisted fabrication of highly homogenized reduced graphene oxide/alumina metacomposites with negative permittivity

Abstract

Graphene oxide (GO) was used to fabricated the highly homogenization reduced graphene oxide (RGO)/alumina (Al2O3) metacomposites with low percolation threshold and adjustable negative permittivity by spark plasma sintering method. Compared to the dry grinding method used for the graphene(GR)/Al2O3 and GR/AlN metacomposites reported in our previous work, the highly homogenization RGO/Al2O3 metacomposites were obtained based on freeze-drying. The microstructures and phase composition of the RGO/Al2O3 metacomposites were investigated by field emission scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The dielectric properties including permittivity (ε′ and ε′′), dielectric loss tangent (tan δ), alternating current conductivity (σac) and reactance (Z′′) were discussed in detail. The percolation phenomenon of σac was observed when the content of RGO increased from 13.50 to 15.38 wt%, and the percolation threshold fitted by the power law was 14.31 wt%, which appeared earlier than the reported GR/Al2O3 and GR/AlN metacomposites. What's more, the negative permittivity behavior was observed when the content of RGO reached 13.50 wt%, which was ascribed to the formation of continuous three-dimensional RGO network among the metacomposites. The RGO13.50/Al2O3 and RGO15.38/Al2O3 metacomposites realized the ε′ transition from negative to positive at 501 and 299 MHz, corresponding to the capacitive-inductive conversion.