Effects Of Sintering Atmosphere On Phase Transformation, Microstructure And Physical Properties Of Fe-Doped Titania

Iron doped titania sols were prepared by sol-gel method, the film of which were coated on the quartz glass and the ceramic substrates with printed comb-like Ag electrode. The films were sintered at different temperatures and different atmosphere to construct photoabsorbtion and humidity sensor components respectively. Phase composition and lattice parameter of titania powders sintered at different temperatures and different atmosphere were analyzed by an X-ray diffraction method; the optical absorption properties of the films were analyzed by a UV-vis spectrometer, the effects of sintering temperature, sintering atmosphere and doping on optical absorption properties of thin films were studied; the valence of ions and surface morphology of the films were respectively studied by an X-ray photoelectron spectroscopy and an atomic force microscopy; the humidity sensing properties of films were analyzed by using an intelligent LCR equipment.Results show that iron ion doping inhibits the transformation of gel to anatase, and first improves then inhibits the transformation of anatase to rutile in reduction atmosphere. The transition temperature of anatase to rutile is increased in reduction atmosphere, from 400℃in oxidation atmosphere to 600℃in reduction atmosphere. The iron ion completely enters in the lattice of titania by the form of substitution in the reduction atmosphere, but it can not entirely solutes into crystal lattice, precipitating phase of Fe₂O₃ when sintering in the oxidation atmosphere.Sintering temperature, sintering atmosphere and iron doping have an influence in optical absorption of films. The doping makes their absorption spectrum have a red shift in different extents, sintering in reduction atmosphere is better than in oxidation atmosphere, and sintering at 700℃and 12mol%Fe doping has the maximum absorption wavelength of 420nm. The corresponding band gap is reduced from 3.46eV to 2.95eV for the undoped film. Ionic valence and surface morphology has a certain impact on the light absorbing properties.The impedance of titania film decreases when sintering in reduction atmosphere; Fe-doping makes the humidity sensing performance improve. While the impedance response to the humidity hardly find when sintering in oxidation atmosphere.