Study of the structure and properties of Pb–Zn borophosphate glasses

Multicomponent oxide glasses of composition 25PbO–25ZnO–xB2O3–(50−x)P2O5, series A, and yPbO–(50−y)ZnO–20B2O3–30P2O5, series B, are investigated. The role of compositional changes on their density, chemical durability, thermomechanical properties and Raman scattering is examined. Structural changes are found to be more pronounced in the series A glasses affecting most thermomechanical properties of the glasses. Raman spectra reveal a continuous shift in frequency of the main vibrational band from 1170 cm−1 at x=0, to 960 cm−1 at x=40, explained in terms of a successive transformation of metaphosphate (Q2) units into pyrophosphate (Q1) and orthophosphate (Q0) units. In the series B of glasses, results show that mixed Pb–Zn borophosphate glasses (y=25) have better chemical durability than end point (y=0, y=50) composition single-cation glasses. With an increasing PbO content, Tg is found to slowly decrease and the thermal expansion coefficient to increase. The frequency shift of the main Raman band from 1092 cm−1 (at y=0) to 1011 cm−1 (at y=50) is ascribed to differences in chemical bonding, coordination numbers and field strength of both cations.