NMR and Raman Studies of Na2O-P2O5-SiO2 Glasses

The 29Si and 31P nuclear magnetic resonance (NMR) chemical shifts and the Qn distribution in ternary sodium phosphosilicate glasses were examined. In the NaPO3-SiO2 glasses, only the Si(Q4) unit from SiO2 and the P(Q2) unit from NaPO3 are observed. When the P2O5 content increases at fixed mole fractions of SiO2 equal to 0.1 and 0.05, the 6-coordinated silicon atoms appear. The presence of 6-coordinated silicon atoms is expected in glasses where the [P2O5]/[Na2O] composition ratio is greater than unity. Their appearances can be understood in terms of the relative acidic strength of SiO2 and P2O5. The profile of Raman spectra changes appreciably due to the formation of 6-coordinated silicon atoms.