Preparation of Iron Networks Hosted in Porous Alumina with Tunable Negative Permittivity and Permeability

• Published in: Advanced functional materials Vol. 23; no. 33; pp. 4123 - 4132
• Main Authors: Shi, Zhi-cheng, Fan, Run-hua, Yan, Ke-lan, Sun, Kai, Zhang, Meng, Wang, Cheng-guo, Liu, Xiang-fa, Zhang, Xi-hua
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 06.09.2013; WILEY‐VCH Verlag
• Subjects: Aluminum oxide; Dielectric constant; dielectrics; double negative materials; Iron; metal-insulators; metal/ceramic composites; metamaterials; Networks; Particulate composites; Permeability; Permittivity; Reduction
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201202895

Random composites of iron particles hosted in porous alumina were prepared from a facile impregnation‐reduction process. Interestingly, when the iron content exceeds the percolation threshold, the interconnection of iron particles results in the formation of iron networks. The composites then change from capacitive to inductive and the conductive mechanism changes from hopping conduction to metal‐like conduction. The negative permittivity was attributed to the plasma oscillation of delocalized electrons in iron networks, while the negative permeability could be ascribed to the strong diamagnetic response of current loops in iron networks. The negative permittivity behavior of the iron/alumina composite was analyzed using Drude model. Additionally, the fitting results indicated that the effective plasma frequency of the iron/alumina composite is much lower than bulk iron. Further investigations show that, the iron content and reduction temperature can easily tune the amplitude and frequency ranges of the negative permittivity and permeability. Moreover, the negative permittivity region and the negative permeability region can be pushed to the same frequency region by adjusting the iron content and reduction temperature. The impregnation‐reduction process opens a new way for the realization of tunable negative permittivity and permeability in random composites, and has great potential for the preparation of new types of double negative materials. Iron particles are hosted in porous alumina via a facile impregnation‐reduction process. When the iron content exceeds the percolation threshold, iron networks are formed. The iron content and reduction temperature can easily tune the amplitude and frequency range of the negative permittivity and permeability. The impregnation‐reduction process has great potential for the preparation of random composites with tunable double negative properties.