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 30 min 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 5–10 mol% WO3 and 5–15 mol% CdO. However, for the ternary TeO2–WO3–CdO system the formation of δ-TeO2 phase was determined in a wider compositional range.