Structure - Properties study of Na2O-CaO-PbO-P2O5 metaphosphate glasses

Sodium-calcium-lead phosphate glasses having a mol.% composition (25-z/2)Na2O-(25-z/2)CaO-zPbO-50P2O5 (0 < z < 50) were prepared by using the melt-quench technique. Some physical properties have been measured and their structure has been studied by IR and Raman spectroscopies. Density of the glass increases linearly with the substitution of Na2O and CaO by PbO. Glass molar volume vary slightly with the substitution, and a nonlinear increase of PbO molar volume and a non-linear decrease of P2O5, Na2O and CaO ones is observed. Glass transition temperature increases non-linearly with PbO substitution. FTIR and Raman spectra reveal the formation of P-O-Pb bonds, which replace P-O-Na and P-O-Ca bonds, and no modification of the network polymerization is observed with substitution by PbO. However, Raman spectra exhibit shoulder's peak due to (PO3)2- terminal groups, which seemingly results from disproportionation of species in the glass melts. PbO is assumed to play a network modifier role like Na2O and CaO, but it reticulates the phosphate network, which causes an increase of Tg and a slight effect on molar volume.