Abstract: Silicon oxynitride and oxide glasses are studied with self consistent field discrete variational X_α(SCF-X_α-DV), one of the molecular orbital calculating methods in quantum chemistry. The chemical bonding is studied to discuss the different properties between silicon oxide glass and the glass in which a part of oxygen atoms are substituted by nitrogen atoms. The difference of properties between silicon oxynitride and oxide glasses is not mainly from the difference of stretching force constant, or of ionic bond strength between Si-N and Si-O bonds. The main reason why silicon oxynitride glass possesses better chemical durability and higher elastic modulus than silicon oxide glass lies in the fact that the covalent bond of Si-N is stronger than that of Si-O, and the bending force constant of N-Si N bond is larger than that of the O-Si-O bond.

Key words: silicon oxynitride and oxide glasses, structure and property, quantum chemistry calculating