Structural evolutions in polymer-derived carbon-rich amorphous silicon carbide

The detailed structural evolutions in polycarbosilane-derived carbon-rich amorphous SiC were investigated semiquantitatively by combining experimental and analytical methods. It is revealed that the material is comprised of a Si-containing matrix phase and a free-carbon phase. The matrix phase is amorphous, comprised of SiC₄ tetrahedra, SiC_xO_x-4 tetrahedra, and Si-C-C-Si/Si-C-H defects. With increasing pyrolysis temperature, the amorphous matrix becomes more ordered, accompanied by a transition from SiC₂O₂ to SiCO₃. The transition was completed at 1250°C, where the matrix phase started to crystallize by forming a small amount of β-SiC. The free-carbon phase was comprised of carbon nanoclusters and C-dangling bonds. Increasing pyrolysis temperature led to the transition of the free carbon from amorphous carbon to nanocrystalline graphite. The size of the carbon clusters decreased first and then increased, while the C-dangling bond content decreased continuously. The growth of carbon clusters was attributed to Ostwald ripening and described using a two-dimensional grain growth model. The calculated activation energy suggested that the decrease in C-dangling bonds is directly related to the lateral growth of the carbon clusters. (Graph Presented).