The TeO2‐Na2O System: Thermal Behavior, Structural Properties, and Phase Equilibria

Abstract

Thermal behavior, structural properties, and phase equilibria of the (100−x)TeO2‐xNa2O system were studied in the 5 ≤ x ≤ 50 mol% composition range. Investigation of glass formation behavior in the binary system was realized, and the glass formation range was determined as 7.5 ≤ x ≤ 40 mol%. Differential thermal analysis (DTA) and Fourier transform infrared (FTIR) spectroscopy techniques were used for thermal and structural characterization of the glasses. Influence of Na2O content on glass transition temperature (Tg), glass stability (∆T), density (ρ), molar volume (VM), oxygen molar volume (VO), and oxygen packing density (OPD) values of sodium tellurite glasses was evaluated considering the structural transformations in the glass network. For the phase equilibria studies, DTA, X‐ray diffraction (XRD), and scanning electron microscopy/energy dispersive X‐ray (SEM/EDS) techniques were utilized to characterize the heat‐treated samples. According to the phase equilibria studies, three eutectic regions were detected in the 0 < x < 50 mol% composition range of the (100−x)TeO2‐xNa2O system. A new invariant endothermic reaction was detected for the compositions between 40 ≤ x ≤ 45 mol%. Na2O.8TeO2 (11.11 mol% Na2O) compound that was claimed to exist in the binary system in the literature was found to be the metastable δ‐TeO2 phase.