Effect of hydrolysis catalyst on the Ti deficiency and crystallite size of sol-gel-TiO₂ crystalline phases

We prepared sol-gel titania by using different hydrolysis catalysts, and characterized it by x-ray powder diffraction. The structure of the crystalline phases—brookite, anatase, and rutile—in the samples annealed between 70 and 900 °C was refined by using the Rietveld technique. From the refinement we obtained the structure parameters, the concentration of each phase, and their average crystallite size. These quantities and their evolution with temperature depended on the hydrolysis catalyst. Anatase and rutile were deficient in Ti, suggesting that their crystalline structure contained hydrogen atoms, forming OH⁻ ions inside. In anatase this deficiency depended on its crystallite size, but it was constant in rutile. When anatase was annealed, it dehydroxylized, producing either crystallitc growing up or its conversion into rutile. From the analysis we also found the conditions for obtaining single-phase samples that could be used as precursors for making up titania single-phase thin films.