Abstract
ABSTRACTStructure and physical properties of 25CaO–xPbO–(75–x)P2O5 (0≤x≤35) glasses are investigated in this paper. Substitution of PbO for P2O5 in the binary 25CaO–75P2O5 glass was found to increase the density and to decrease the molar volume. Fourier transform infrared (FTIR) and Raman spectroscopies show the evolution of the phosphate skeleton when the PbO content increases: Q3 to Q2 species (0<x≤25) and Q2 phosphate network (x = 25) to short phosphate groups (x > 25) such as (P4O136−) (x = 35). The glass transition temperature first decreases with x, then increases for x values larger than 10%. The evolution of the glass transition temperatures is interpreted from the structural data: the minimum point observed in Tg is attributed to the transition of the ultraphosphate network from the network containing the modifying cations at isolated sites to a network with modifier sub-structure sharing terminal oxygens. At higher PbO content, the large increase in Tg is due to the reticulation of the phosphate network by PbO4 groups.
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