Structure and properties of ZnO–B2O3–P2O5–TeO2 glasses

Zinc borophosphate glasses doped with TeO2 were studied in the compositional series (100 − x)[0.5ZnO–0.1B2O3–0.4P2O5]–xTeO2 in a broad concentration range of x = 0–80 mol% TeO2. The structure of the glasses was studied by Raman and IR spectroscopy and by 31P and 11B MAS NMR spectroscopy. According to the Raman and IR spectra, TeO2 is incorporated in the structural network in the form of TeO3, TeO3+1 and TeO4 structural units. The ratio of TeO4/TeO3 increases with increasing TeO2 content in the glasses. The incorporation of TeOx units into the glass network is associated with the depolymerisation of phosphate chains, as revealed by Raman spectroscopy. The incorporation of TeO2 modifies also the coordination of boron atoms, where B(OP)4 structural units are gradually replaced by B(OP)4−n(OTe)n units. The addition of TeO2 to the parent zinc borophosphate glass results in a decrease of glass transition temperature associated with the replacement of stronger P–O and B–O bonds by weaker Te–O bonds. Chemical durability of glasses reveals a minimum at the glass containing 10 mol% TeO2, but with further additions of TeO2 it improves and the glasses with a high TeO2 content reveal better durability than the parent zinc borophosphate glass.