Stability of the δ-TeO₂ phase in the binary and ternary TeO₂ glasses

The stability of δ-TeO₂ phase was studied in binary TeO₂-WO₃, TeO₂-CdO and ternary TeO₂-WO₃-CdO glasses. The samples were prepared by heating high purity powder mixtures of TeO₂, WO₃ and/or CdO to 800°C in a platinum crucible with a closed lid, holding for 30min and quenching in water bath. Differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterize the thermal, phase and microstructural properties of the δ-TeO₂ phase. The addition of CdO into the tellurite glasses increased the stability range of the δ-TeO₂ phase up to higher temperature values and expanded the compositional δ-TeO₂ formation range. The formation of δ-TeO₂ phase in the binary systems was observed for samples containing 5-10mol% WO₃ and 5-15mol% CdO. However, for the ternary TeO₂-WO₃-CdO system the formation of δ-TeO₂ phase was determined in a wider compositional range.