Microstructure and EMW absorbing properties of SiC_nw/SiBCN-Si₃N₄ ceramics annealed at different temperatures

SiC nanowire/siliconboron carbonitride-Silicon nitride (SiC_nw/SiBCN-Si₃N₄) ceramics were prepared via a low-pressure chemical vapor deposition and infiltration (LPCVD/CVI) technique. The as-prepared ceramics were annealed at varying temperatures (1200–1600 °C) in a N₂ atmosphere, and their crystallization mechanism and absorbing properties were subsequently studied. The absorbing properties of the SiC_nw/SiBCN-Si₃N₄ ceramics improved with the annealing temperature up to a certain value and decreased thereafter. Among the samples tested, the SiC_nw/SiBCN-Si₃N₄ ceramics annealed at 1300 °C showed the highest permittivity (real and imaginary parts) and dielectric loss values in the X-band (ca. 5.34, 2.55, and 0.47 respectively), and this could be attributed to the precipitation of carbon and SiC nanocrystals. The sample treated at 1300 °C decreased its minimum reflection coefficient (RC) from −12.0 to −59.68 dB (compared with the as-received SiC_nw/SiBCN-Si₃N₄ ceramics) and the effective RC (below -10 dB) in the whole X-band could be achieved when the thickness was set to 3–3.5 mm. These results revealed that the absorbing performance was significantly improved after the heat treatment at 1300 °C.