Thermal properties and stability of TeO2 containing phosphate glasses

Differential thermal analysis and thermodilatometry have been used to study the thermal behaviour of glasses in the ZnO–P2O5–TeO2 system prepared in 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. The addition of TeO2 to the starting zinc metaphosphate glass resulted in a gradual increase of thermal expansion coefficient from 12.2 up to 16.6 ppm °C−1, whereas glass transition temperature and dilatometric softening temperature reveal a minimum at the glass with x = 30 mol% and y = 10 mol % TeO2. All glasses crystallize on heating within the temperature range ∼500–700 °C. The contribution of the surface crystallization mechanism over the internal one increases with increasing TeO2 content. Major compounds formed by crystallization were Zn(PO3)2 and Zn2P2O7.