Abstract

Nanostructured TiO2-SnO2 thin films and powders were prepared by a facile aqueous particulate sol-gel route. The prepared sols showed a narrow particle size distribution with hydrodynamic diameter in the range 17.2-19.3 nm. Moreover, the sols were stable over 5 months, since the constant zeta potential was measured during this period. The effect of Sn:Ti molar ratio was studied on the crystallisation behaviour of the products. X-ray diffraction analysis revealed that the powders were crystallised at the low temperature of 400 A degrees C containing anatase-TiO2, rutile-TiO2 and cassiterite-SnO2 phases, depending on annealing temperature and Sn:Ti molar ratio. Furthermore, it was found that SnO2 retarded the anatase to rutile transformation up to 800 A degrees C. The activation energy of crystallite growth was calculated in the range 0.96-6.87 kJ/mol. Transmission electron microscope image showed that one of the smallest crystallite sizes was obtained for TiO2-SnO2 binary mixed oxide, being 3 nm at 600 A degrees C. Field emission scanning electron microscope analysis revealed that the deposited thin films had nanostructured morphology with the average grain size in the range 20-40 nm at 600 A degrees C. Thin films produced under optimized conditions showed excellent microstructural properties for gas sensing applications. They exhibited a remarkable response towards low concentrations of CO gas at low operating temperature of 200 A degrees C, resulting in increased thermal stability of sensing films as well as a decrease in their power consumption.