In recent years, random composites with negative permittivity have been widely concerned owing to their unique properties and broad application prospects. In this paper, Ti 3 C 2 T x /carbonized wood (CW) composites with weakly negative permittivity were prepared by using CW as matrix and two-dimensional layered Ti 3 C 2 T x as the functional filler. The results of dielectric properties indicated that when the content of Ti 3 C 2 T x was 42.5 wt%, three-dimensional conductive networks were formed universally on the surface and inside the CW matrix. Meanwhile, the conduction mechanism changed from jumping conduction to metal-like conduction. Besides, the permittivity values of Ti 3 C 2 T x /CW composites changed from positive to negative and significantly reduced to the range of −65 to −35. This unique phenomenon was owing to the total electron concentration in the Ti 3 C 2 T x /CW composite being diluted equivalently, resulting in the decrease of plasma frequency, thus showing a weakly negative permittivity. This work provides a new strategy to determine the suitable content of conductive filler using percolation theory. Furthermore, the original fantastic structure properties of Ti 3 C 2 T x and wood also opened a new way for designing metacomposites, which has very important research value and far-reaching research significance. Graphical abstract Weakly negative permittivity achieved in two-dimensional Ti 3 C 2 T x /carbonized wood metacomposites.
Guohua Fan,Xiaoping Zhang,Qingyu Wang,Ran Su,Yanan Tang,Chuncheng Hao,Yao Liu
Ceramic composites made up of well-selected components have enriched the varieties of the metamaterials with negative electromagnetic parameters. In this work, TiN/BaTiO 3 ceramic composites were prepared with a simple dry-pressing and pressureless sintering process. Percolation was eventually determined to be the key inducements which caused the permittivity of the ceramic composites changing from positive to negative. Essentially, negative permittivity was closely related to the plasma oscillations of free electrons in percolation networks. Meanwhile, conduction mechanism of the composites varied owing to the changes in microstructure, where the percolation networks brought out pathways for electron migration and achieved high conductivity. In addition, ac impedance behavior with changes of the sign for reactance were also discussed, thus the transition from electrical capacitive to inductive for the percolative ceramic composites has been demonstrated. This work clarified the influence of percolation on the conductivity, impedance, and permittivity of ceramic composites altogether. The obtained negative permittivity composites have enormous potential in various electronic devices and electromagnetic apparatus.
A bio-gel derived strategy was used to construct Ni/C nanocomposites consisting of three-dimensional (3-D) carbon networks with embedded nickel nanoparticles. The amorphous carbon prevents agglomeration of the nickel nanoparticles and thus contributes to a good impedance match. The microwave absorption properties of the Ni/C nanocomposites were optimized according to percolation theory for good impedance matching. As a result, microwave absorbing coatings, which have the advantages of thin thickness (1.75 and 1.5 mm) and light weight (25 and 30 wt%), were achieved with excellent absorbing properties (90% microwave absorption) and a broad bandwidth (13.6–18 GHz and 13.2–18 GHz). The absorbing properties were mainly attributed to the dielectric relaxation processes at 2–18 GHz from the multilevel interface, porous carbon materials and nanoscale nickel nanoparticles in the Ni/C nanocomposites. It is believed that this work not only helps to elucidate the mechanism of absorption but also provides a new design paradigm for determining the optimal content of absorbers using percolation theory. The bio-gel derived strategy paves a possible way for the mass synthesis of microwave absorbers.
危险品化学品经营许可证（带存储）