MOLECULAR-DYNAMICS STUDY OF NA-SI-O-N OXYNITRIDE GLASSES

The structure and properties of Na-Si-O-N oxynitride glasses have been studied by molecular dynamics calculations using a pair potential of-the Busing approximation of the Born-Mayer-Huggins type. Nitrogen atoms bonded to one, two, and three silicon atoms coexist in the glass structure. The mean of the number of silicon atoms bonded to a nitrogen atom ranges from 2.4 to 2.1, decreasing with increasing Na2O content from 15 to 30 mol%. It has been assumed that nitrogen atoms bonded to two or fewer silicon atoms are formed when nitrogen atoms substitute for non-bridging atoms. The bond angle angle Si-N-Si exhibits a bimodal distribution around 105-135-degrees and 140-170-degrees, roughly corresponding to the nitrogen atoms bonded to three and two silicon atoms, respectively. The dependences of the density, the bulk thermal expansion, and the bulk modulus on the nitrogen content are consistent with those observed in real systems.