MODIFICATION OF THE PHASE-TRANSITION TEMPERATURES IN TITANIA DOPED WITH VARIOUS CATIONS

Titania matrices prepared by a sol-gel technique were doped with sever al cations (La, Zn, Al, K, Na, Ca, Ba, and Co). The effect of the dopa nts on the thermal and structural properties of the materials is analy zed. The dopant concentration was 2% mol with respect to titanium, and in all cases the same anion (nitrate) was used. The transition temper atures from amorphous to anatase and from anatase to rutile were measu red using x-ray diffraction. The amorphous-anatase transition is indep endent, for almost all samples, of the type of dopant used; however, t he 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 f ound a correlation between the anatase-rutile phase transition tempera ture and the radius of the cations and their electric charge.