Study Of Transformation Behavior Of La～(3+)/Ce～(3+)-Doped TiO₂/ZnO Gels

Different contents of Zn²⁺-doped titania gels and different contents of rare earth La³⁺/Ce³⁺-doped TiO₂/ZnO compound gels were prepared by the sol-gel method. The effects of Zn²⁺-doping and La³⁺/Ce³⁺-doping on transformations of gels to anatase and anatase to rutile, as well as the crystal granularity were characterized by using techniques such as TG-DTA and XRD.Experimental results show that the transformation of gels to annatase of pure TiO₂ occurs at about 400℃, and anatase to tutile occurs at about 500℃; Zn²⁺-doping can effectively depress the phase transformations of gels to anatase and anatase to rutile, enhancing the transition temperatures and sufficiently inhibiting the growth of anatase crystals. For the TiO₂/ZnO compound gels, Ce³⁺-doping can accelerate the phase transformations of gels to anatase, but depress the phase transformation of anatase to rutile and sufficiently inhibit the growth of anatase crystal obtaining nanocrystals. La³⁺-doping also accelerate the phase transformations of gels to anatase, but depress the phase transformation of anatase to rutile at 500℃and 600℃, and the transformation temperature of anatase to rutile is first enhanced and then depressed at 700℃, indicating that different contents of RE ion-doping make different influence to transformations of TiO₂/ZnO compound gel.There are two effects of RE-doping on TiO₂ growth and transformation. Less RE ion doping can enter TiO₂ crystal lattice and form oxygen vacancy, so that it is benefit to TiO₂ growth and transformation; but more RE ion doping can enter TiO₂ crystal lattice making distortion of the lattice, and the distortion energy can depress transformation. On the other hand, more doping makes the RE oxide cover TiO₂ grains so it depresses the growth and transformation of TiO₂ grains, and increase crystal grain size. Therefor, different contents of RE ion-doping can take different influence to TiO₂ phase transformations.