Transformation Behavior Of Ion-doped TiO₂ Based Composite Gels And Humidity Sensing Properties Of Thin Films

Composite gels and thin films of Sn²⁺-doped TiO₂, La³⁺/Ce³⁺-doped TiO₂-20wt%SnO₂ were prepared by the sol-gel method. The transformation process of composite gels was investigated by XRD, TG-DTA techniques, the relative content of rutile and granularity were analyzed. Besides, humidity sensing properties of thin films were tested, and the effect of ions doping were investigated.Experimental results show that, the transformation temperatures of gels to anatase appear at about 400℃, and anatase to rutile at about 500℃for pure TiO₂. The transformation temperatures of gel to anatase and anatase to rutile first decrease and increase and then decrease with the increase of the ionic content for Sn²⁺-doped TiO₂ and La³⁺-doped TiO₂-20wt%SnO₂. The transformation temperatures of gel to anatase first increase and decrease and then increase, and that of anatase to rutile always increase with an increase of the ionic content for Ce³⁺-doped TiO₂-20wt%SnO₂.Sn²⁺, La³⁺and Ce³⁺ doping restrained the growth of anatase and rutile, moreover, the granularity decreased with the increase of doping content. There are very complex effects of Sn²⁺, La³⁺ and Ce³⁺ doping on the transformations from gel to anatase and from anatase to rutile, which depressed the transformation of gel to anatase when sintered at 400℃, Sn²⁺ doping improved the transformation of anatase to rutile, La³⁺ doping first depressed and then improved, Ce³⁺ doping first improved and then depressed when sintered at 500℃, while Sn²⁺ doping first depressed and then improved the transformation of anatase to rutile, La³⁺ and Ce³⁺doping depressed when sintered at 600℃. La³⁺ and Ce³⁺ doping, stimulated the transformation of SnO₂ phase at the same time.Sn²⁺, La³⁺ and Ce³⁺ doping decrease the electric resistance of TiO₂ based films, presenting better linearity in the humidity-resisrance relations to some extent, which is related to the granularity decrease of anatase and rutile due to Sn²⁺, La³⁺ and Ce³⁺ doping, as well as the adhibition of crystal defect in anatase and rutile and that of phase boundary in thin films.