The TeO ₂ ‐Na ₂ O System: Thermal Behavior, Structural Properties, and Phase Equilibria

Thermal behavior, structural properties, and phase equilibria of the (100− x )TeO ₂ ‐ x N a ₂ O 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 Na ₂ O content on glass transition temperature ( T _g ), glass stability (∆ T ), density (ρ), molar volume ( V _M ), oxygen molar volume ( V _O ), 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 )TeO ₂ ‐ x N a ₂ O system. A new invariant endothermic reaction was detected for the compositions between 40 ≤ x ≤ 45 mol%. Na ₂ O.8TeO ₂ (11.11 mol% Na ₂ O) compound that was claimed to exist in the binary system in the literature was found to be the metastable δ‐TeO ₂ phase.