engleski

X-ray powder diffraction investigation of Fe-doped TiO2 samples synthesized by the sol-gel method under alkaline conditions

Titania, TiO2, is a technologically interesting material because of its catalytic and electronic properties. Its properties, however, change when it is doped with metal atoms or when prepared to have a very small crystallite size [R. J. H. Clarc, The Chemistry of Titanium and Vanadium, Elsevier Publ. Co., New York, 1968]. In this work we examined the influence of iron doping on structural properties of titania. Polycrystalline titania and Fe-doped titania samples containing 0.5, 1.1, 2.6, 8.1 and 18 at% Fe were prepared by a sol-gel technique. Ti(IV)-isopropoxide and Fe(III)-nitrate were used as precursors of titanium and iron. Synthesis was performed in a nitrogen inert atmosphere under alkaline conditions, which was accomplished by addition of NH3. As-synthesized samples were annealed at 500 °C for 2 hours. The samples were examined by X-ray powder diffraction at room temperature. Sample of pure titania was anatase (tetragonal, S. G. I41/amd). Sample with 0.5 at% Fe was an anatase-type solid solution. For Fe doping level higher than 0.5 at% Fe the samples contained two phases, that of anatase-type and of rutile-type (tetragonal, S. G. P42/mnm), respectively. Anatase phase was dominant for all the doped samples. The sample with 18 at% Fe contained impurity, namely ~5% Fe2TiO5. All the samples were nanocrystalline, with crystallite sizes in the range 10-20 nm. Diffraction line broadening increased with Fe doping level. Unit-cell parameters were determined using Si as an internal standard, and refined by the whole powder pattern fitting [WPPF program, H. Toraya, J. Appl. Cryst. 19 (1986) 440]. Iron doping increased slightly unit-cell parameters of both anatase- and rutile-type phases. The Rietveld method [H. M. Rietveld, J. Appl. Cryst. 2 (1969) 65] was performed to refine the crystal structure of obtained phases, and the real incorporation level of Fe into the anatase and rutile lattices was determined.

TiO2; XRD; Rietveld method

nije evidentirano