Tunable Electromagnetic Properties in Co/Al2O3 Cermets Prepared by Wet Chemical Method

Cobalt/alumina composites with three-dimensional cobalt networks hosted in porous alumina matrix were prepared by a facile impregnation process under low temperature. The effects of composition and microstructure on their electromagnetic properties were investigated. A percolation phenomenon appeared with cobalt content increasing, and an interesting feature of negative permittivity was obtained in the percolative composites due to the appearance of equivalent inductances, while the composites were equivalent to circuit models composed of capacitance and resistance with Co content below the percolation threshold. Meanwhile, negative permeability was obtained in the frequency range of 500 MHz ~ 1 GHz. Further investigations showed that the electromagnetic properties of the composites could be changed significantly when the cobalt particles networks turned into sheet structure. That was to say, the electromagnetic properties of metal–ceramic composites could be tailored by their compositions and microstructures, which make it available for microwave-absorbing materials, attenuation ceramics and microwave dielectrics, etc.