Titania matrices prepared by a sol-gel technique were doped with several cations (La, Zn, Al, K, Na, Ca, Ba, and Co). The effect of the dopants on the thermal and structural properties of the materials is analyzed. The dopant concentration was 2% mol with respect to titanium, and in all cases the same anion (nitrate) was used. The transition temperatures from amorphous to anatase and from anatase to rutile were measured using x-ray diffraction. The amorphous-anatase transition is independent, for almost all samples, of the type of dopant used; however, the anatase-to-rutile phase transition depends strongly on the kind of cation. This means that the temperature range where the anatase phase exists can be controlled by choosing the appropriate dopant. We have found a correlation between the anatase-rutile phase transition temperature and the radius of the cations and their electric charge.
Sols of titania were obtained by the sol-gel method and their size profile was followed by dynamical light scattering. In the early stages of the reaction an unstable behavior was detected. After this unstable regime the particle size reaches a steady state where the sols have a constant size while increasing in number. Once the sol concentration reaches its overlap value, the gelation regime takes place. For samples prepared in this way Raman spectra and x-ray diffractometry were used to characterize the kinetics of crystallization of the material.
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