Enhanced electrical resistivity in SiC–BN composites with highly-active BN nanoparticles synthesized via chemical route

In order to fabricate SiC–BN composites with enhanced electrical resistivity, boric acid and urea were used as reactants for synthesizing nano-sized BN particles on the surfaces of SiC powders in flowing ammonia atmosphere. The composites containing 10 wt% BN were pressureless densified at 2150   °C for 1   h with B 4 C and C as sintering additives. The chemical route was advantageous for obtaining finer BN dispersoids and microstructures of higher homogeneity, which significantly enlarged the SiC/BN interdiffusion area. Consequently, the concentrations of dissolved B and N in SiC grains became more equivalent and the carrier concentration was further decreased through impurity compensation mechanism. The chemically processed composite exhibited a considerably high electrical resistivity (1.03   ×   10 12   Ω   cm), which was ∼15 times higher than that of the composite prepared by conventional powder mixing method. Besides, considerably low dielectric constant (13.88) and loss tangent (0.128) at 1   MHz, as well as good thermal conductivity (70.08   W   m −1   K −1 ) were also achieved.