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In this paper, boron-doped dense 6H-SiC ceramics was fabricated by the high-temperature physical vapor transport (HTPVT) method. The effect of B doping on the crystal structure stability of 6H-SiC was investigated based on density functional theory (DFT). The results show that B doping can be realized even under thermodynamical equilibrium conditions. Nevertheless, it is found that the B doping effects on the (0001) of Si-plane and (000-1) of C-plane are significantly different. The doping experiments demonstrated that B can observably change the crystal growth morphology, leading to the formation of elongated 6H-SiC crystals.

Dense silicon carbide (SiC) ceramics were prepared by the high-temperature physical vapor transport (HTPVT) method at 2300°C using three types of graphite materials, namely common graphite (CP), isostatic graphite (IG), and graphite paper (GP), as crucible lids. The results indicated that the nucleation of SiC on CG was much easier than that on GP at the initial stage, but the polycrystalline growth on GP was faster. Moreover, the polycrystalline SiC ceramics growing on CG and IG lids were smaller than that grown on GP lid because many pores appeared at the interfaces between the grown polycrystalline SiC and CG and IG lids. As a result, the strength of the grown dense SiC ceramics on GP lid was about 8%–20%, higher than the strength of ceramics grown on the CG and IG lids.