Broadband dielectric and conductivity spectra of dielectric — Metal nanocomposites for microwave applications

Three kinds of dielectric-metal nanocomposites were prepared and studied: a) epoxy resin-xFe (x = 0-30 vol.% is a content of the Fe nanoparticles); b) epoxy resin-xNi (x = 0-40 vol.% is a content of the Ni nanoparticles); c) paraffin-xFe (x = 10^-60 vol.% is a content of the Fe nanoparticles). Their dielectric and ac conductivity spectra were measured in a broad frequency range from 10^-2 Hz to 1010 Hz. Dielectric/conductivity dispersion was observed in the whole frequency range. Increase of the metal content results in the increase of the composite dielectric permittivity, loss and conductivity in the whole frequency range. The power-law dispersion of conductivity and permittivity characterizes response in the microwave range for all studied composites. For the compositions with high metal content, above the percolation threshold, the conductivity plateau screens the power-law dispersion at low frequencies. Three contributing polarization/conductivity mechanisms are considered, possibilities of the composites microwave applications are discussed.