Two percolation behaviors in binary heterogeneous composites for high permittivity and negative permittivity

Percolative composite is usually studied to achieve high permittivity when the fraction of fillers reaches the percolation threshold; besides, negative permittivity has also been a research hotpot and can be obtained above the percolation threshold. However, no studied have been carried out to clarify whether the two percolation behaviors are the same one and whether only one percolation threshold exists. In this paper, the binary heterogeneous composites consisting of TiN particles and epoxy were prepared by compression molding, their dielectric performance and percolation behavior were studied in detail. Two percolation behaviors were demonstrated with increasing the TiN content. The first percolation behavior is to describe the high permittivity while the second one is to describe negative permittivity. The dielectric constant firstly increased with increasing filler content and thus high permittivity was achieved near the first percolation threshold, further increasing the filler content made the dielectric constant decrease but still kept positive, gradually the dielectric constant turned negative when the filler content was above the second percolation threshold. The equivalent circuit analysis demonstrated that the competitive effect between inductance and capacitance is the main reason for the two percolation behaviors, which was further attributed to the change of microstructure of composites. This work presents a clear physical description for the percolation phenomenon in the view of dielectric performance of heterogeneous composite.