Influence of secondary oxide phases on microstructural and gas sensitive properties of nanostructured titanium dioxide thin films

A systematic comparison of single and binary metal oxide T1O₂, TiO₂-Ga₂O₃, TiO₂-Er ₂O₃ and TiO₂-Ta₂O₅ gas sensors with nanocrystalline and mesoporous microstructure, prepared by sol-gel route, was conducted. The gas sensitivity was increased by secondary phase introduction into TiO₂ film via two mechanisms, firstly through the inhibition of anatase-to-rutile transformation, since the anatase phase accommodates larger amounts of adsorbed oxygen, and secondly through the retardation of grain growth, since the higher surface area provides more active sites for gas molecule adsorption. The binary metal oxides exhibited a remarkable response towards low concentrations of CO and NO₂ gases at low operating temperature of 200°C, resulting in increasing thermal stability of sensing films as well as decreasing their power consumption. The calibration curves revealed that all sensors followed the power law (S = A[gas]^B) (where S is sensor response, coefficients A and B are constants and [gas] is gas concentration). The response magnitude of the sensors obtained in this work is superior to TiO₂-based sensors reported in previous studies.