The TeO2-rich part of the TeO2–Ga2O3 system: equilibrium and non-equilibrium phase diagram

Abstract

The TeO₂-rich part of the TeO₂–Ga₂O₃ system has been investigated, under equilibrium and non-equilibrium conditions, by temperature programmed X-ray diffraction and differential scanning calorimetry (DSC). Two invariant equilibria have been detected: one peritectic reaction and one eutectic reaction. The peritectic reaction corresponds to the incongruent melting at 620 °C ± 5 °C of the crystalline compound Ga₂Te₄O₁₁ (ΔH_P = 18.1 ± 2 kJ mol⁻¹) and to the equilibrium Ga₂Te₄O₁₁ ↔ L_P + Ga₂O₃. The eutectic reaction (23 mol% GaO_1.5, T_E = 600 ± 5 °C, ΔH_E = 22.2 ± 2 kJ mol⁻¹) corresponds to the equilibrium TeO₂ + Ga₂Te₄O₁₁ ↔ L_E. The glass forming domain ranges from 5 to 30 mol% GaO_1.5, and can be extended from 0 to 35 mol% by quenching the melt in a freezing mixture, consisting of ice, ethanol and NaCl (≈−14 °C). The thermal behaviour of glasses has been studied. The glass transition and crystallization temperatures, and the phases which appear during the crystallization have been identified.