Crystallization Behavior of Amorphous Si₂BC₃N Ceramic Monolith Subjected to High Pressure

The crystallization behavior of amorphous Si₂BC₃N monoliths by heating at 1000°C-1400°C and 5 GPa was investigated with the special attention to the nucleation mechanisms of β-SiC and BN(C) phases. Nanoscale puckered structures arising in particle bridging areas were found and its evolution behavior well reflected the nucleation process of nanocrystallites. The temperature-dependent crystallization of amorphous Si₂BC₃N monoliths at 5 GPa passes through four stages: The material remains amorphous below 1100°C. It undergoes partial phase segregation (1100°C-1200°C), followed by initiation of nucleation (1200°C-1250°C), and then nucleation and growth of β-SiC and turbostratic BN(C) crystallites (>1250°C). The first principles calculation indicates the nucleation precedence of BN(C) phase over β-SiC. BN(C) nucleates preferentially at bridges between ceramic particles causing SiC to concentrate in particle interiors thus forming capsule-like structures.