Sol - Gel Synthesis, Characterization and Optical Properties of TiO2/TeO2 powders

The present investigation deals with the sol-gel synthesis and optical characterization of gels in the binary TiO2 - TeO2 system. Titanium butoxide and telluric (VI) acid (H6TeO6) were used as main precursors for preparation of the rich in TiO2 (above 35 mol %) compositions. The heat treated up to 300 degrees C gels are predominantly amorphous and contain small amount of metallic tellurium. Several crystalline phases TiTe3O8, TeO2, TiO2 (anatase) and TiO2 (rutile) simultaneously exist above this temperature. Two maxima about 230 - 250 nm and 290 - 330 nm related to the isolated TiO4 units and condensed TiO6 groups, respectively were observed in the UV - Vis spectra. The heating of all samples above 500 degrees C led to an increase of the UV absorption peak at 330 nm (instead of that at 230 nm) which is related to the greater condensation processes. In comparison to the pure Ti butoxide gel, a red shifting of the absorption edge for samples containing up to 50 mol % TeO2 was observed, while composition containing higher TeO2 amount (above 50 mol %) exhibited blue shifting.