New silicon nitride-based electromagnetic metamaterial with industrial potential

Electromagnetic metamaterials with negative physical parameters such as negative dielectric constant and negative magnetic permeability have attracted widespread attention in the academic community. In 2010, they were praised by Materials Today as one of the top ten advances in materials science in the past 50 years. Different from traditional electromagnetic materials, they exhibit negative refractive index, perfect imaging and super absorption, and are widely used in optical stealth, wireless communication, electromagnetic wave absorption and shielding. Introducing randomly distributed carbon or metal conductive phases into insulating matrix is ​​one of the important methods for preparing metamaterials. Silicon nitride ceramics are considered to be an ideal matrix for preparing metamaterials due to their high insulation, high thermal conductivity, high temperature resistance, corrosion resistance and excellent comprehensive mechanical properties. However, the preparation of silicon nitride-based metamaterials is currently limited to pressure-assisted sintering processes and porous matrix impregnation processes. Pressure-assisted sintering, such as spark plasma sintering and hot pressing sintering, has low production efficiency, and the product shape and size are also greatly restricted. It is not suitable for industrial scale-up, and the toughness is poor due to the inability of silicon nitride grains to be fully developed. The porous impregnation process requires that the matrix have a high porosity to facilitate full infiltration of the second phase, which seriously affects the mechanical properties of the material, weakens the high strength and toughness advantages of silicon nitride ceramics, and limits its application potential in some harsh service conditions, such as high load, oxidation, corrosion, and wear environments.

Recently, a team of material scientists from Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences used tungsten particles as the second phase and proposed a new silicon nitride-based metamaterial that can be densified without mechanical pressure. This material not only has a high degree of densification and the preparation process is suitable for industrial scale-up, but also the silicon nitride grains grow and develop, maintaining the advantage of high toughness. This has important guiding significance for the preparation and industrial application of high-performance metamaterials.

The team published their work in Journal of Advanced Ceramics on January 17, 2025.

“Previous studies have found that metallic tungsten is a second phase that matches the thermal expansion of silicon nitride ceramics. Although it will react chemically with silicon nitride at high temperatures, our research has found that the appropriate nitrogen pressure can effectively inhibit the chemical reaction, creating conditions for the introduction of metallic tungsten. With the assistance of gas pressure, we successfully introduced tungsten into silicon nitride ceramics, and found that the introduction of tungsten had a positive effect on the mechanical and tribological properties of silicon nitride ceramics. More importantly, the melting point of metallic tungsten is extremely high. After introduction, it will not produce molten agglomeration during the sintering process of silicon nitride, and it does not have a significant negative impact on the sintering activity of silicon nitride like carbon materials. This makes it possible to achieve the densification preparation of silicon nitride metamaterials without the assistance of mechanical pressure by introducing tungsten. Based on the previous work, this work first proposed the use of metallic tungsten as a conductive metal phase to study the preparation of high-performance silicon nitride-based metamaterials, analyzed and solved the problem of decreased densification of silicon nitride ceramics at high tungsten content, and observed the negative dielectric constant behavior of the material when the metal tungsten content reached 20vol%. For the first time, the densification preparation of silicon nitride-based metamaterials was achieved without the assistance of mechanical pressure.” said Lujie Wang, associate researcher at the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, an expert whose research interests focus on the field of silicon nitride ceramics.

After 20 vol% content of tungsten was introduced, tungsten particles interconnect to form conductive pathways and the composite becomes conductive. In addition, the random distribution of tungsten particles changes the permittivity of the composites significantly, and a negative permittivity behavior was observed in the frequency range of 40-50 MHz. A dense silicon nitride-based metamaterial with industrial potential was proposed and prepared, guiding the industrial exploration and application of high-performance metamaterials.

“Metamaterials have great potential for application in optical stealth, and we hope that our materials can be used in this regard. Our next step will be to continue to optimize the composition and structure and explore the realization of its dielectric constant characteristics in a wider frequency range.” said Lujie Wang.

Other contributors include Zhuhui Qiao from the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences in Lanzhou, China; Xuejian Liu, Dewei Ni, Hui Zhang, Jie Yin, Zhengren Huang from Shanghai Institute of Ceramics, Chinese Academy of Sciences in Shanghai, China; Qian Qi from Shandong University of Science and Technology in Qingdao, China.

This work was supported by National Natural Science Foundation of China (No. 52102080), Youth Science Foundations of Gansu Province (23JRRA598), and Shandong Provincial Natural Science Foundation (No. ZR2020ZD29, ZR2021JQ20). The authors would like to acknowledge Xuemei Song at Shanghai Institute of Ceramics for SEM performance and Xiaojie Song at Shandong University of Science and Technology for TEM performance.

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in “Materials Science, Ceramics” category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508

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