Experimental realization of tunable negative permittivity in percolative Fe78Si9B13/epoxy composites

Abstract

Negative permittivity is one of the most important properties in the realization of double negative medium or negative index materials. In this paper, tunable negative permittivity in the radio frequency range has been obtained in composites with Fe₇₈Si₉B₁₃ amorphous alloy dispersed in an epoxy matrix. The microstructure and dielectric properties of Fe₇₈Si₉B₁₃/epoxy composites are investigated in detail. The results indicate that when the Fe₇₈Si₉B₁₃ content is beyond the percolation threshold, the plasma oscillation of delocalized electrons in interconnected Fe₇₈Si₉B₁₃ leads to negative permittivity. By controlling the effective concentration of free electrons, the negative permittivity of the Fe₇₈Si₉B₁₃/epoxy composites could be easily adjusted. Additionally, the frequency dispersion behaviors of the conductivity conform to the Jonscher's power law below percolation threshold, demonstrating that the conductive mechanism is hopping conduction. The realization of tunable negative permittivity in Fe₇₈Si₉B₁₃/epoxy composites gives a new and high-efficient way toward double negative materials.