Synthesis, characterization and crystalline phase studies of TeO2–Ta2O5–ZnO/ZnF2 oxyfluoride semiconducting glasses

•TeO2–Ta2O5–ZnO glasses by substituting ZnO with ZnF2 were synthesized.•Structural, thermal and optical characterizations were performed.•The presence of new Zn4Ta2O9, Ta2Te2O9, ZnTa2O6 crystalline phases were confirmed. Changes that occur related to structural, optical and thermal properties of TeO2–Ta2O5–ZnO glass by substituting ZnO with ZnF2 were investigated. Oxyfluoride semiconducting glasses were prepared with melt-quenching technique according to 80TeO2-4Ta2O5-(16-x)ZnO–xZnF2 (x = =0,4,8,12,16 mol%) composition. Optical properties of synthesized glasses were determined with UV–vis spectrophotometer; structural properties determined with X-Ray diffraction, FTIR, Raman and 19F NMR; thermal properties determined with DSC. Glass network was determined to consist of TeO4tbp, TeO3tp structural units, and conditions of Zn and Ta within the structure were also examined. It was observed that thermal stability increased with increasing amount of fluoride, and various exothermic bands and peaks were present in DSC thermograms. These peaks and crystalline phases at temperature values corresponding to these bands were examined in detail for 8%ZnO+8%ZnF2 sample. According to this, in addition to known ZnTeO3, ZnTe3O8 crystalline phases, the presence of Zn4Ta2O9, Ta2Te2O9, ZnTa2O6 crystalline phases were also confirmed at certain temperatures.