Heterogeneity in iron-doped titania flower-like nanocrystalline aggregates: detection of brookite and anatase/rutile size–strain modeling

Abstract

Detailed investigations of Raman spectra and X-ray powder diffraction (XRPD) patterns of rutile-rich and anatase/brookite-poor flower-like nanocrystalline aggregates of Fe-doped TiO 2 shed new light with regard to its microstructure and heterogeneity. The brookite phase has been detected from the Raman spectra, and the presence of different phases in pure and doped samples is discussed. The phonon confinement model (PCM) was applied to Raman spectra, and the Warren-Averbach and simplified integral breadth methods were applied to XRPD patterns in order to obtain information about the nanocrystallite size and strain of rutile and anatase. The applied methods (i.e. XRPD size-strain analysis and the PCM fit of Raman spectra), when used in combination and together with other experimental techniques like highresolution transmission electron microscopy, could be very useful in nanomaterial characterization.

Resonance Raman spectroscopic study for radial vibrational modes in ultra‐thin walled TiO2 nanotubes

“…The shift and broadening of the Raman peaks observed in this study suggest the presence of size effects and can be attributed to the phonon confinement and gross structural disorder with presence of strain in the as‐grown nanocrystalline phase. Similar effect was also observed for the anatase TiO 2 nanoclusters with positive dispersion in the phonon dispersion curve and its line shape for the E g mode . No other peaks corresponding to rutile or any other TiO 2 polymorphs are seen in the spectra, in good agreement with XRD results.…”

“…Similar effect was also observed for the anatase TiO 2 nanoclusters with positive dispersion in the phonon dispersion curve and its line shape for the E g mode. [22][23][24][25] No other peaks corresponding to rutile or any other TiO 2 polymorphs are seen in the spectra, [26] in good agreement with XRD results. We observe a mixture of modes, which are vibrating along the radial axis, three E g(ν1, ν5, ν6) and normal to it, two B 1g(ν2, ν4) and A 1g(ν3) .…”

“…(b)]. The unusual large background may be due to the gross structural disorder in the samples effective with ultraviolet excitation . We observe symmetry allowed modes of E g(ν6) at 643 cm −1 and its second‐order overtone, 2 E g(ν6) at 1330 cm −1 .…”

“…The unusual large background may be due to the gross structural disorder in the samples effective with ultraviolet excitation. [23,24] We observe symmetry allowed modes of E g(ν6) at 643 cm À1 and its second-order overtone, 2E g(ν6) at 1330 cm À1 . In this context, we must state that the band gap of our sample was found to bẽ 3.27 eV from diffused spectroscopic measurement (absorption data typically shown in supplementary Fig.…”

Assessment of the Cr doping and size effects on the Raman‐active modes of rutile TiO2 by UV/Visible polarized Raman spectroscopy

“…Our results rather indicate that the changes described in the preceding texts in the positions and intensity of the Raman peaks, as well as the appearance of new modes in the Raman signal of the Cr-doped samples, are directly related neither to size effects nor with polarization effects, but they are associated with the presence of Cr. As the wavenumber of the vibrational modes depends on the force constants of the Ti─O bonds, the effects observed in the Raman spectra should be induced by structural distortions and strain [32] due to the incorporation of Cr in the lattice. The background intensity of the Raman spectra could be influenced by the disorder at the surface of the analysed samples, although no significative variations with Cr amount have been observed in this work.…”