Heterogeneity and Disorder in Ti_1−xFe_yO_2−d Nanocrystal Rutile-Based Flowerlike Aggregates: Detection of Anatase

Abstract

Here we report results of systematic investigation of heterogeneity and disorder in Ti 1-x Fe y O 2-d nanorod rutilebased flowerlike aggregates. It was found that Ti 1-x Fe y O 2-d aggregates are composed of two crystalline phases: rutile as a dominant and anatase as a minor phase. Flowerlike aggregates were found to grow from an isometric core ca. 5-10 nm in diameter that was built from anatase and rutile nanorods ca. 5 Â 100 nm that were grown on the anatase surface having base plane (001) intergrowth with an anatase plane. The direction of rutile nanorods growth, i.e., direction of the nanorod elongation, was [001]. Highly nonisometric rutile crystals produce anisotropic X-ray powder diffraction line broadening and doubling of vibrational bands in Raman spectra. Both these techniques confirmed nonisometric character of rutile crystals and gave a quantitative measure of crystal shape anisotropy in excellent agreement with high-resolution transmission electron microscopy measurements. In addition, from the atomic pair distribution function and Raman spectral analyses the level of vacancy concentration was determined in rutile and anatase phases of investigated samples.

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.…”

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

“…Notably, some authors (Mazza et al, 2007) have reported that the PCM is not an adequate method for explaining the features of the lattice dynamics in rutile nanocrystals. However, satisfactory PCM fits of the Raman spectra of the rutile phase have been obtained here, and the results are presented and compared with previous Raman, HRTEM and XRPD results (Kremenović et al, 2011). The most intense anatase and rutile E g modes were modeled by the PCM in order to estimate the dimensions of the anatase nanoparticles, as well as the diameters of the rutile nanorods.…”

“…However, they are systematically different from values obtained by the Thompson-Cox-Hastings pseudo-Voigt function (TCH-pV) parameter method (e.g. in pure TiO 2 the size and strain are 10 nm and 2 Â 10 À3 , respectively), especially for the crystallite size (Kremenović et al, 2011). The crystallite sizes obtained in the [110] direction by the WA and SIB methods are almost three times smaller than the average values (over all directions) obtained from the TCH-pV parameter method, while the RMSS values are about the same.…”

“…This motivated the study of iron-doped TiO 2 nanocrystals to determine details of their composition, structure, microstructure and morphology (Kremenović et al, 2011). It was reported that synthesized samples with 0, 0.22, 0.47 and 1.05 at.% of iron in TiO 2 predominantly crystallized in rutile form with small amounts of anatase and no brookite.…”

Enhanced hydrogen evolution from water splitting using Fe-Ni codoped and Ag deposited anatase TiO2 synthesized by solvothermal method

“…However, this scattering peak exhibits a slight shift to the high frequency for the metal modified TiO 2 (Fig. 3a), the shifts from 144 cm −1 for pure TiO 2 to 150 cm −1 for Fe-Ni/Ag/TiO 2 is observed, this results from the defect effects and surface interaction between metal and TiO 2 [41,45,46]. In addition, other four vibration peaks at 398, 514, 639 cm −1 and a weak shoulder at 196 cm −1 are corresponded to B 1g(1) , A 1g ,+B 1g(2) , E g (2) and E g (3) for all samples in Fig.…”