New investigations within the TeO2-rich part of the Tl2O–TeO2 system

Abstract

The phase diagram TeO₂–Tl₂TeO₃ has been studied under equilibrium and non-equilibrium conditions by differential scanning calorimetry and temperature programmed X-ray diffraction. Four crystalline phases, three stable (Tl₂TeO₃ , α-Tl₂Te₂O₅ , Tl₂Te₃O₇) and one metastable (β-Tl₂Te₂O₅) have been identified and characterized. The three stable phases decompose peritectically at 377, 315 and 342 °C respectively. β-Tl₂Te₂O₅ , which is formed by cooling of a melt, undergoes a monotropic transformation into the stable α polymorph. This study also confirmed the existence of a large glass-forming domain (15–52 mol% TlO_0.5). The complex thermal behaviour of these very stable glasses has been studied. The glass transition and crystallization temperatures, and the nature of crystalline phases formed, have been determined.