Molecular dynamics simulation of amorphous silicon nitride containing B and C, was carried out in order to investigate the short-range atomic arrangement and diffusion behavior. In amorphous Si-B-N, B atoms were in a nearly threefold coordinated state with N atoms, while B atoms in amorphous Si-B-C-N had bonding with both C and N atoms. Carbon atoms in Si-B-C-N were also bonded to Si atoms. The self-diffusion constant of N in Si-B-N became much smaller than that in amorphous Si3N4. Also, amorphous Si-B-C-N exhibited smaller self-diffusion constants of constituent atoms, even compared to Si-B-N. Addition of B and C was important in decreasing atomic mobility in amorphous Si-B-C-N. This may explain the increased thermal stability of the amorphous state observed experimentally.

Atomic Structure and Diffusion in Amorphous Si-B-C-N by Molecular Dynamics Simulation. K.Matsunaga, Y.Iwamoto, Y.Ikuhara: Materials Transactions, 2002, 43[7], 1506-11. See also: Journal of the American Ceramic Society, 2001, 84[10], 2213-9