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

The effect of different cations in the anatase–rutile phase transition temperatures 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 state, the atomic size, etc. on these temperature modifications. Linear relationships between the anatase–rutile phase transition temperatures and the ionic radii for alkali metal, alkaline earth metal, and group 3 and 13 elements 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 temperature 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 same anion (nitrate) was used for all salts. A variation of more than 330 °C in the anatase–rutile phase transition temperatures was obtained by using these dopants. The transition temperatures from amorphous to anatase and from anatase to rutile phases were obtained from the x-ray diffractograms.