Structural and optical characterization of the crystalline phase transformation of electro spinning TiO₂ nano fibres by high temperatures annealing

The electro spinning technique has been used to synthesize TiO₂ nano fibres, which by annealing at high temperatures achieves the crystalline phase transformation of anatase to rutile passing through the anatase-rutile mixed. The investigated temperature range was 0-1000 degrees Celsius. The TiO₂ nano fibres surface morphology and chemical stoichiometry were obtained by Scanning Electron Microscopy and Energy Dispersive Spectrometry. The annealed nano fibres diameter was ranged from 137.0 to 115.3 nm in the investigated temperature range. The influence of the annealing temperature on the structure and crystalline phase quality of the TiO₂ nano fibres has been investigated by X-ray diffraction and Raman scattering. Clear evidence have been obtained of the structural transformation of TiO₂ nano fibres from pure anatase to pure rutile, including the almost amorphous and anatase-rutile mixed structural phases by X-ray diffraction and confirmed by Raman scattering. By X-ray diffraction was found that the TiO₂ nano fibres crystalline phases presented as preferential growth direction (101) for anatase and (110) for rutile. The Raman spectroscopy exhibits the anomalous behavior for band broadening and shifting of Raman bands with increasing crystallite size that forms the nano fibres. The room-temperature photoluminescence presents radiative bands whose dominant band redshifts from 2.56 to 1.32 eV, as the crystalline phase is transformed by annealing at high temperature. (Author)