Negative permittivity behavior of carbon fibre/alumina ceramic composites prepared by hot-press sintering

Although metals are the most common conductive functional phase in metacomposites preparation, onedimensional carbon fibre (CF) is an ideal alternative. In this paper, ceramic composites with CFs homogeneously dispersed in an alumina matrix were prepared using a hot press sintering process. The impact of CF contents on the microscopic morphology, electrical conductivity and negative permittivity behavior of the composites was systematically investigated. The conductivity of the composites increased with increasing CF contents, and their impedance modulus subsequently decreased. The conductivity mechanism of the composites transformed from a hopping conductivity to a metal-like conductivity. With the increase in CF contents above the percolation threshold, the composites showed a negative permittivity behavior at the frequency range from 1 kHz to 10 MHz. The negative permittivity of the metacomposites was attributed to the plasma oscillations of free electrons in the three-dimensional CF networks, and the corresponding dispersion characteristics were in agreement with the Drude model. The plasma oscillation frequencies of ceramic composites moved to higher frequencies with increasing CF content in the composites, and the absolute value of negative permittivity also increased. These findings can be useful for clarifying the realization and regulation mechanism of negative permittivity, which greatly facilitates the development of ceramic-based metacomposites.