Controlling physical and sensing properties of nanostructured titanium dioxide by erbium oxide

Nanocrystalline and mesoporous TiO2–Er2O3 films and powders with various TiO2:Er2O3 molar ratios have been prepared by a sol–gel route. X-ray diffraction and Fourier transform infrared spectroscopy revealed that erbium oxide formed in the range 50–100 mol.-%Er2O3, whereas erbium dititanate formed in the range 25–100 mol.-%Er2O3. Oxygen deficient titania phases (TiO2-x), such as Ti7O13 and Ti2O3, were observed for TiO2:Er2O3=25:75 (molar ratio) system annealed at 800ºC. It was observed that Er2O3 retarded anatase to rutile transformation. Furthermore, TEM analysis also showed that Er2O3 hindered the crystallisation and crystal growth of powders. Atomic force microscope (AFM) analysis confirmed that TiO2:Er2O3=75:25 (molar ratio) system annealed at 600ºC produced the smallest grain size (17 nm) and the highest roughness. Moreover, TiO2:Er2O3=50:50 (molar ratio) system annealed at 800ºC showed the smallest grain size (32 nm) and the highest roughness. The sensing properties of TiO2 films were improved by introducing Er2O3 phase into the sensing film. The fabricated sensors showed stable, reliable and reproducible response with small response and recovery times towards CO and NO2 gases. The working temperature of the sensors was reduced down to 200ºC, and therefore they can be used for industrial application.