Molecular dynamics study of atomic structures in amorphous Si-C-N ceramics

Molecular dynamics (MD) simulations based on Tersoff interatomic potentials have been carried out for amorphous silicon carbonitride (Si-C-N) ceramics. Short-range atomic arrangements and self-diffusion behavior in Si-C-N are investigated. In the Si-C-N amorphous network with homogeneously distributed carbon atoms, silicon atoms are bonded to both nitrogen and carbon atoms, forming mixed tetrahedra of Si (C, N)₄. The average coordination number of C to Si is nearly three, which is larger than that of N to Si. The calculated self-diffusion coefficient of Si decreases with increasing carbon content in the Si-C-N systems. This indicates that C atoms play a role in reducing atomic diffusivities in Si-C-N at high temperatures, which may explain the observed thermal stability of Si-C-N amorphous ceramics.