Structure and properties of glasses in ZnO–P2O5–TeO2 system

Glasses in the ternary ZnO–P2O5–TeO2 system were prepared and studied in two compositional series (100 − x)[0.5ZnO–0.5P2O5]–xTeO2 (X-series) and 50ZnO–(50 − y)P2O5–yTeO2 (Y-series) within the concentration range of x = 0–60 and y = 0–40 mol% TeO2. Their structure was studied by Raman and 31P MAS NMR spectroscopies. The incorporation of TeOx units into the structural network is associated with the depolymerisation of phosphate chain structure as revealed by both methods. At a high TeO2 content isolated PO4 tetrahedra are formed in the structure of glass series Y, while diphosphate O3P–O–PO3 groups are present in the structure of the glass series X. In the structure of glass series Y tellurium atoms form predominantly TeO3 trigonal pyramids, whereas in the X glass series TeO4 trigonal bipyramids prevail in the glass structure. The addition of TeO2 to the parent zinc metaphosphate glass results in a decrease of glass transition temperature in both compositional series associated with the replacement of stronger P―O bonds by weaker Te―O bonds.