Negative permittivity behavior in percolative molybdenum/alumina composites

Metal-ceramic composites with excellent electrical, mechanical and thermal properties can be as an outstanding candidate for electromagnetic metamaterials. In this work, alumina cermet with percolation Mo networks was utilized to construct an intrinsic metamaterial, thereby realizing a negative permittivity behavior at the radio-frequency band. In an effort to explore the origin of this negative dielectric property, Drude-Lorentz model was developed to explain the dielectric response of Mo/Al2O3 cermets, revealing that the negative permittivity resulted from low frequency plasmonic states of unbound electrons in conductive Mo networks and the isolated Mo particles would also make contribution to the frequency dispersion of negative permittivity at the same time. Besides, a percolation phenomenon appeared in cermets with raising Mo content, and the conduction behavior was analyzed by percolation theory, showing a transition of conductive mechanism from hopping conduction to metal-like conductive behavior. Our obtained cermets with negative permittivity offer the potential to lead to advances in intrinsic metamaterials.