Dielectric and EMW absorbing properties of PDCs-SiBCN annealed at different temperatures

Polymer derived SiBCN ceramics (PDCs-SiBCN) were prepared from polyborosilazane and then annealed at 1200-1800°C in N₂. Effects of annealing temperature on the microstructure, phase composition, dielectric and wave-absorbing properties of ceramics were investigated. Results showed that nano-sized SiC grains were formed in amorphous SiBCN after annealing and the content and crystallization degree of SiC gradually intensified with annealing temperature increasing. The permittivity, dielectric loss and electrical conductivity of PDCs-SiBCN gradually increased as the temperature rose due to the formation of conductivity network of SiC grains and the increase of nano-grain boundary. The increased content of SiC (as the dipole) and interface between SiC nano-grains and amorphous SiBCN phase led to a higher polarization ability and higher dielectric loss. The RC gradually decreased with the annealing temperature increasing, demonstrating the annealed ceramics had the superior wave-absorbing ability and high annealing temperature was conducive to the improvement of wave-absorbing property.