Percolative cobalt/silicon nitride composites with tunable negative electromagnetic parameters

In this paper, the relationship between the microstructures and electromagnetic properties of cobalt/silicon nitride (Co/Si3N4) composites synthesized by an impregnation-calcination process are discussed. The enhanced interconnectivity of cobalt particles led to the appearance of percolation phenomenon and the change of conductive mechanism from hopping conduction to metal-like conduction. The composites above percolation threshold exhibited the negative permittivity and negative permeability behavior, which were mainly ascribed to the plasma oscillation of free electrons and the diamagnetic responses of conductive cobalt network, respectively. The frequency region and magnitude of such negative electromagnetic parameters closely associated with the cobalt content. When the cobalt content reached 35 wt%, simultaneous negative permittivity and negative permeability were realized in the frequency range from 550 MHz to 1 GHz. The experimental exploration of Co/Si3N4 composites by tailoring compositions and microstructures has great significance on the development of tunable negative electromagnetic parameter materials.