Thermal study of the anatase–rutile structural transitions in sol-gel synthesized titanium dioxide powders

Titanium dioxide powders were synthesized by the sol-gel process using titanium tetrabutoxide as the precursor. The syntheses were performed in saturated aqueous solutions of KCl, CaCl2 ,N iCl 2 ,C oCl 2 and MnCl2, and in dimethyl- formamaide (DMF) and dimethylsulfoxide (DMSO) solutions. The obtained X-ray diffraction patterns show that all samples were crystalline (anatase phase) with some minor amounts of a brookite phase. It is worth noting that the anatase phase was ob- tained independent of any previous or further treatment of the synthesized powder, such as hydrothermal or heat treatment. For the titanium dioxide powders synthe- sized in saturated aqueous solution of metal chlorides (mean crystallite size = 11 nm), the anatase-rutile transition occurred in the range 455-570 °C, depending on the considered sample, as verified by DTA analysis. In the powders synthesized in DMF or DMSO solutions (means crystallite size = 6 nm), the same structural transi- tion occurred at 485°C.