Sol-gel synthesis of composites in the ternary TiO2-TeO2-B2O3 system

The gel formation region in the ternary TiO2-TeO2-B2O3 system has been determined. Transparent monolithic gels are obtained for compositions between 30 and 100 mol% TiO2, up to 65 mol% TeO2 and 75 mol% B2O3. Titanium butoxide, telluric (VI) acid and boric acid were used as precursors. Differences were observed in the degree of decomposition of Ti butoxide in the presence of H3BO3 and H6TeO6 acids. The phase transformations of the obtained gels in the temperature range 200-700 degrees C were investigated by XRD. Composite materials containing an amorphous phase and different crystalline phases (metallic Te, alpha-TeO2, anatase, rutile and TiTe3O8) were prepared. IR results show that the short range order of the amorphous phases, which are part of the composite materials, consist of TiO6, BO3, BO4, and TeO4 structural units. Since free B2O3 is not detected in the three-component amorphous compositions, it is suggested that they have a better connectivity between the building units compared to binary TiO2-B2O3 compositions. The UV-Vis spectra of the as-prepared gels exhibited a red shift of the cut-off due to the presence of boron and tellurium units.