G. Antonioli

Raman study of nanosized titania prepared by sol–gel route

Abstract TiO 2 polycrystalline powders have been prepared by different sol–gel routes and have been investigated by Raman spectroscopy and transmission electron microscopy. The influence of different catalysts on the crystalline phases obtained by thermal annealing is studied. The mechanisms that determine the Raman line shapes are discussed, including phonon confinement and pressure effects. The analysis of the Raman spectra, after thermal treatments in air and N 2 , indicates the importance of the non-stoichiometry due to oxygen vacancies.

Nanocrystalline α-Fe2O3 sol-gel thin films: a microstructural study☆

Abstract The structure of α-Fe 2 O 3 sol-gel thin films, obtained from an alkoxide precursor, was investigated by X-ray diffraction, X-ray absorption spectroscopy and conversion electron Mossbauer spectroscopy. Samples heated at 300°C were amorphous, while those treated at 400 and 500°C showed the presence of crystalline hematite. The crystallites were small enough to give rise to the superparamagnetic effect. In the nanostructured films, the α-Fe 2 O 3 particles were not linked together but dispersed in a network of amorphous ferric oxide.

X-ray absorption spectroscopy study of crystallization processes in sol-gel-derived TiO2☆

Abstract Sol-gel-derived bulk amorphous TiO2 and the crystalline phases obtained by heat treatments are investigated by X-ray absorption spectroscopy. The environment of the Ti atoms in the amorphous phase shows a residual from the alkoxide precursor and the presence of anatase crystallites. Thermal treatments up to 350°C give crystalline anatase and the pure rutile phase is obtained at 750°C. Near-edge absorption measurements confirm the octahedral coordination of Ti in all the phases investigated.

Fe2O3 films for Ξ(3) optics: Raman and XAS characterization

Two different sol-gel syntheses, both starting from inorganic salts as precursors, Fe(NO 3 ) 3 . 9H 2 O or FeCl 3 . 6H 2 O, have been employed to prepare, by dip-coating, films of α-Fe 2 O 3 , which are currently investigated for their high non-linear optical susceptibility X (3) . Thermal treatments at 500°C lead to the α-Fe 2 O 3 hematite structure for both preparations as indicated by XRD and Raman, Information on the differences in the local order between the two preparations are obtained by X-ray absorption spectroscopy (XAS) measurements.

IR and EXAFS analysis of xBi2O3 · (1 − x)GeO2 glasses

The glassy system xBi2O3 · (1 − x)GeO2 with high bismuth content (x = 0.9) has been investigated by infrared spectroscopy in the range 200–4000 cm−1 and by extended X-ray absorption fine structure (EXAFS) spectroscopy at the Ge absorption K-edge. The infrared measurements show that the addition of Bi2O3 to GeO2 causes a shift and splitting into two components of the band associated with the stretching mode occurring in the GeO4 tetrahedra. This result is accounted for by assuming that Bi atoms perturb the environment around GeO4 units rather than change the oxygen coordination around germanium from fourfold to sixfold. A tetrahedral coordination for germanium atoms at all bismuth concentrations is found from the EXAFS analysis. The role of the preparation procedure on the glass infrared transmission is discussed.

Coordination changes in telluro-vanadate glasses containing ZnO or CdO

Abstract The structure around the metal ions in x TeO 2 xa0·xa0(1xa0−xa0 x )V 2 O 5 , x ZnOxa0·xa0(1xa0−xa0 x )V 2 O 5 , x ZnOxa0·xa0(1xa0−xa0 x )[2TeO 2 xa0·xa0V 2 O 5 ] and x CdOxa0·xa0(1xa0−xa0 x )[2TeO 2 xa0·xa0V 2 O 5 ] glasses has been investigated by Raman and X-ray absorption fine structure (XAFS) spectroscopies. In x TeO 2 xa0·xa0(1xa0−xa0 x )V 2 O 5 , the coordination of Te changes from TeO 4 to TeO 3 with increasing x . The main effect of the addition of modifier oxides in vanadate and telluro-vanadate glasses is a transformation of the VO 5 bi-pyramids to VO 4 tetrahedra. No apparent change in the local structure around the modifier atoms is revealed by XAFS measurements.

X-ray absorption study of titanium coordination in sol-gel derived TiO2

Abstract Sol-gel derived TiO2 in amorphous form is investigated by X-ray absorption spectroscopy. Anatase micro-crystallites and residuals of the alkoxide precursor are found in the glass and no evidence of tetrahedrally coordinated titanium may be inferred from the XANES spectra. Pure crystalline phases are obtained by thermal treatments.

Bond strengths in defect chalcopyrite ZnGa2Se4 by temperature dependence of EXAFS

Abstract We present a study of the temperature dependence of EXAFS (Extended X-Ray Absorption Fine Structure) Debye-Waller-like factor in defect chalcopyrite ZnGa 2 Se 4 at the Ga and Zn K-absorption edges. The EXAFS Einstein frequencies relative to the bonds between cation atoms and the nearestneighbour chalcogen atoms are considered. The results indicate that the Gaue5f8Se bond is about 15% softer than the Zue5f8Se bond: this is discussed on the basis of the vibrational spectrum of ZnGa 2 Se 4 . The approach used demonstrates that EXAFS T -dependent spectra can be useful in obtaining quantitative values for the effective bond strengths in complex materials.

Fe2+-O and Mn2+-O bonding and Fe2+- and Mn2+-vibrational properties in synthetic almandine-spessartine solid solutions: an X-ray absorption fine structure study

X-ray absorption fine structure (XAFS) measurements at the Fe and Mn K-edges were undertaken to investigate the Fe2+-O and Mn2+-O bonding, and Fe2+- and Mn2+-vibrational properties for a series of synthetic almandine-spessartine, (Fe,Mn)(3)Al2Si3O12, garnet solid solutions. The two end members almandine, Fe3Al2Si3O12, and spessartine, Mn3Al2Si3O12, and three solid solutions of composition Alm75Sps25, Alm50Sps50 and Alm25Sps75 were studied at different temperatures between 77 K and 423 K. The spectra show that the state of alternating bonds provides an appropriate description for the two crystallographic ally independent X-O(1) and X-O(2) bonds in the solid solution. An exchange of X-site cations in garnet is associated with measurable structural relaxation. The compositional and temperature dependence of the XAFS Debye-Waller factors for Fe2+ and Mn2+ in the plane of the X-O(1) and the X-O(2) bonds were also determined. Their values in the plane of the X-O(2) bonds are greater compared to those for X-O(1) and they do not vary greatly as a function of garnet composition. In the case of end-member spessartine, the XAFS Debye-Waller factors for Mn2+ are compared to the Debye-Waller factors measured from single-crystal X-ray diffraction. An analysis shows correlation in the atomic displacements along the shorter Mn-O(1) bond.

Application of Synchrotron Radiation X-Ray Fluorescence (μ-SRXF) and X-Ray Microanalysis (SEM/EDX) for the Quantitative and Qualitative Evaluation of Trace Element Accumulation in Woody Plants

ABSTRACT Different analytical techniques were applied to describe the localization of lead and chromium in the tissues of walnut (Juglans regia) and maple (Acer saccharinum) plants exposed to soils that had been artificially contaminated with heavy metals. Two X-ray-based techniques, synchrotron radiation X-ray fluorescence (μ-SRXF) and X-ray microanalysis (SEM/EDX), were utilized in association with induced coupled plasma optical emission spectrometry (ICP-OES). These techniques allowed the definition of maps showing a preferential accumulation of lead in the root periderm of both plants and a limited translocation of the metal to the stems. Accordingly, estimation of the lead concentration with ICP-OES showed that roots contained, on a dry weight basis, 20 to 40 times more metal than stems. Chromium, supplied to the plants as Cr3+ or Cr6+, was taken up only in the latter case and in limited amounts. In general, walnut was more efficient than maple in the uptake of lead and chromium. The combination of X...