High-temperature dielectric and microwave absorption properties of Si₃N₄–SiC/SiO₂ composite ceramics

A novel model with low–high–low permittivity hierarchical architecture was designed for high-temperature electromagnetic wave (EM) absorption. Si₃N₄–SiC/SiO₂ composite ceramic was fabricated to verify this model. Dielectric properties of Si₃N₄–SiC/SiO₂ in X-band from 25 to 600 °C were investigated. Due to the special designed structure, the effective permittivity of Si₃N₄–SiC/SiO₂ increases slightly with rising temperature. When the temperature increases from 25 to 600 °C, average \( \varepsilon^{\prime} \) in X-band increases from 5.6 to 6.1, and \( \varepsilon^{\prime\prime} \) increases from 3.0 to 3.8. Because of the weak temperature dependence of effective permittivity, Si₃N₄–SiC/SiO₂ exhibits good coordination between room temperature EM absorption and high-temperature EM absorption. Minimum reflection coefficient (RC) of Si₃N₄–SiC/SiO₂ at room temperature reaches −38.6 dB with the sample thickness of 3.2 mm. At 500 and 600 °C, minimum RC of Si₃N₄–SiC/SiO₂ with certain sample thickness reaches −51.9 and −35.9 dB, respectively. Meanwhile, the effective bandwidth reaches 4.16 and 4.02 GHz, which indicates the promising prospect of Si₃N₄–SiC/SiO₂ for high-temperature EM absorption.