High‐Frequency Negative Permittivity from Fe/Al2O3 Composites with High Metal Contents

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Abstract
For conventional metal/ceramic composites, we report an interesting negative permittivity behavior, which was usually observed in artificial metamaterials. The Fe/Al2O3 composites with different Fe volume contents ranging from 10% to 40% were prepared through hot‐pressing sintering. The impedance and dielectric properties of the composites in high frequency range present a distinct dependence on the composition, and the negative permittivity is obtained when Fe content exceeds 20 vol%. The experimental results of negative permittivity from the composites above percolation threshold are in good agreement with fitting results from Drude model. The tunability of negative permittivity makes Fe/Al2O3 composites promising candidates for the double negative materials.

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