Effect of SiBCN content on the dielectric and EMW absorbing properties of SiBCN-Si₃N₄ composite ceramics

Siliconboron carbonitride ceramics (SiBCN) were introduced into porous Si₃N₄ substrates via low pressure chemical vapor deposition and infiltration from SiCl₃CH₃-NH₃-BCl₃-H₂-Ar system. To improve the electromagnetic wave(EMW) absorbing properties, the molar ratio, n_CH3SiCl3/(n_NH3 + n_BCl3), was increased based on thermodynamics analysis. The results show that nanosized silicon carbide crystals and free carbon dispersed uniformly in the amorphous SiBCN phase, resulting in suitable dielectric properties and improved absorption capabilities of SiBCN-Si₃N₄ ceramics. Additionally, with increasing SiBCN ceramics loading, the amount of nanocrystals and interface between nanocrystals and amorphous SiBCN phase increased, leading to enhanced polarization and dielectric loss of the composite ceramics. When SiBCN content was up to 3.64 wt%, the electromagnetic reflection coefficient (RC) of SiBCN-Si₃N₄ composite ceramics reached −40 dB (>99.97% absorbing) with the effective electromagnetic absorbing bandwidth of 3.64 GHz in the X-band. This study makes it possible to fabricate SiBCN-based composite materials with excellent EMW absorbing properties at a low temperature.