Morphology of rutile and brookite nanocrystallites obtained by X-ray diffraction and Rietveld refinements

Titanium oxide was prepared under hydrothermal conditions from a very acidic solution, with titanium butoxide as titanium precursor and hydrochloric acid as the source of protons; the pH was regulated adding water to this solution. The H₂O/HCl molar ratio was varied from 10 to 50; this ratio, together with the synthesis temperature, which varied between 90 °C and 200 °C, determined the phase concentrations. Samples contained mainly the titania polymorphs rutile and brookite; the highest concentration of this last phase was obtained for the ratio of 20 and the synthesis temperature of 120 °C. The synthesized powder was analyzed with X-ray powder diffraction, refinement of the crystalline structures and transmission electron microscopy. The refinement provided information not only about the average crystallites dimensions but also about their morphologies, which were similar to those observed by transmission electron microscopy. The refinement also shows that the lattice parameters of rutile changed with H₂O/HCl molar ratio and synthesis temperature, while those of brookite were almost constant.