Sol-gel powder synthesis in the TiO2-TeO2-ZnO system: Structural characterization and properties.

The present study deals with the gel formation tendency in the ternary TeO 2 -TiO 2 -ZnO system. Depending on the TiO 2 amount, the gelation occurred at different times and subsequently several gel formation regions have been determined. Homogeneous, transparent and monolithic gels were obtained using combination of organic and inorganic precursors during the synthesis. Using XRD analysis it was established that upon the heating composites were obtained which contain an amorphous phase and different crystalline phases: TiO 2 (anatase), TiO 2 (rutile), α-TeO 2 and ZnTeO 3 , depending on composition. The IR results showed that the short range order of the amorphous phases which are part of the composite materials consist of TiO 6 , ZnO 4 and TeO 4 structural units. Using UV–Vis spectroscopy it was established that the absorption edge of the gels varied from 330 nm to 364 mm and the increase in TiO 2 content caused a red shifting of the cut-off. The calculated Eg values are in the range 3.41–3.75 eV higher than that of pure TiO 2 , TeO 2 and ZnO oxides. The XPS results showed that the Te atoms in the surface layers of the samples studied exist in several chemical states as Te²⁺, Te⁰, but Te⁶⁺ dominates. Octahedrally coordinated Ti⁴⁺ ions are observed in the gels and in the samples annealed at 200 °C but a small amount of tetrahedrally coordinated Ti⁴⁺ is also detected, which indicates the incomplete polymerization of TiO 6 units. [ABSTRACT FROM AUTHOR]