Effects of cationic dopants on the phase transition temperature of titaniaprepared by the sol-gel method

The effect of different cations in the anatase-rutile phase transition temp eratures for titania prepared by the sol-gel method was studied. The metal dopants were chosen from different periods and groups of the periodic table to see the role played by the electronic configuration, the oxidizing stat e, the atomic size, etc. on these temperature modifications. Linear relatio nships between the anatase-rutile phase transition temperatures and the ion ic radii for alkali metal, alkaline earth metal, and group 3 and 13 element s were obtained. For elements of the period 4, there was not such a defined tendency; for most of them the modification of the phase transition temper ature was too small. The cations used were Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+, Al3+, Y3+, La3+, Er3+, Ti4+, Co2+, Ni2+, Cu2+ and Zn2+. In all cases the dopant's concentration was 2 mol% with respect to titanium, and the sam e anion (nitrate) was used for all salts. A variation of more than 330 degr ees C in the anatase-rutile phase transition temperatures was obtained by u sing these dopants. The transition temperatures from amorphous to anatase a nd from anatase to rutile phases were obtained from the x-ray diffractogram s.