Marcello Zocchi

Oxidation of Sn Thin Films to SnO 2 . Micro-Raman Mapping and X-ray Diffraction Studies

The oxidation of tin layers deposited onto alumina substrates is investigated with the aim to identify the different steps of the process and obtain information on the sample homogeneity, phase segregation, and degree of oxidation. It is shown that at least three phases coexist at 450 °C, Sn, SnO, and SnO2, and remarkable inhomogeneities, already visible at an optical inspection, are found in the thin film. A micro-Raman mapping of the layer shows that these inhomogeneities are related to the presence of different Sn oxidation states, as evidenced by the inhomogeneous distribution of SnO and SnOx Raman bands. The thin film becomes homogeneous after annealing treatments above 550 °C, where only the SnO2 cassiterite phase is detected.

Niobium-titanium oxide powders obtained by laser-induced synthesis: Microstructure and structure evolution from diffraction data

The influence of the niobium content on the anatase-to-rutile phase transition in nanopowders of Nb–Ti oxides was studied and the changes in the particle size and microstrain distribution obtained at different temperatures were analyzed. A correlation is found between the initial microstructure in the Ti 1 – x Nb x O 2 ( x = 0.03, 0.2) powder and the niobium content. The presence of Nb was found to inhibit the growth of both the anatase and the rutile phases.

Correlation between crystallite sizes and microstrains in TiO2 nanopowders

Abstract Nanopowders of TiO 2 doped with by V, Nb, Ta were obtained by laser-induced pyrolysis. The profiles of the diffraction peaks were Fourier analysed with a single-peak method and the microstructural parameters 〈 M 〉 (average crystallite size) and 〈 e 2 〉 1/2 (mean-square root microstrain) were estimated. A linear correlation between 〈 e 2 〉 1/2 〈 M 〉 and 1/〈 M 〉 was observed in both anatase and rutile phases. For a given crystallite size, the microstrains as well as the dispersion of data were larger in anatase then in rutile. Indeed, one of the factors inducing the anatase-to-rutile transformation may be the presence of larger microstrains in anatase. In rutile, the high correlation found between 〈 e 2 〉 1/2 〈 M 〉 and 1/〈 M 〉 suggests that in this phase the microstrains present in the structure are due only to the geometrical constraints of the surface. Indeed, for infinite crystallite size no microstrains are expected. In anatase, microstrains depend also on the specific cation present in the crystallite.

Butadiene polymerization with lanthanide catalysts: activity and X-ray diffraction study of neodymium bromide complexes with basic ligands

This paper reports on the study of five neodymium bromide complexes of general formula NdBr3·nL prepared according to the scheme NdBr3·6H2O + 6HC(OCH3)3 → NdBr3·nCH3OH + 6HCO(OCH3) + (12 − n)CH3OH, followed by ligand exchange, leading to neodymium tribromide complexes NdBr3·nL with nL = 4iPrOH (I), 4THF (II), 4Py (III), 2THF (IV) and 2iPrOH (V) where iPr = isopropyl, THF = tetrahydrofuran and Py = pyridine. The catalytic activity of all the above complexes in the polymerization of butadiene is very high and it increases from I to III. The diffraction study of I and II shows that both molecules are monomeric (coordination number 7), indicates that the nature of the NdBr bonds is influenced by ligand substitution, and reveals that the covalent contribution is more important in II than in I. The correlation of these findings with the results obtained from the study on the activity is discussed.

W-TI-O LAYERS FOR GAS-SENSING APPLICATIONS : STRUCTURE, MORPHOLOGY, AND ELECTRICAL PROPERTIES

The kinetics of phase transitions and phase segregation induced by annealing temperature on the Ti–W–O gas-sensing layer was studied by x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The main goal was to identify, on the basis of kinetics studies, structurally stable Ti–WO 3 thin film phases and compare their response to polluting gases in order to determine possible correlations between structural and electrical properties of the sensing layers.

Structural analysis of new basic multifunctional polymers by the comparison method

Abstract A method of structural analysis based on analogies and differences in the X-ray diffraction patterns of unoriented samples of chemically related polymers is proposed. By this method we study a family of new basic multifunctional polymers based on the repeat unit -S-CH 2 -CH 2 -X-CH 2 -CH 2 -S-CH 2 -CH 2 -Y-CH 2 -CH 2 - where the functional groups X and Y can be considered as independent variables. Eleven patterns are compared here and used in the discussion.

The crystal structure of the cesium bronze Cs(Mo0.95W0.05)7O21

Abstract The crystal structure of Cs(Mo0.95W0.05)7O21 has been determined from a single-crystal X-ray diffraction experiment. The crystal is orthorhombic (space group Pnma), with a = 17.638(5), b = 5.448(1), c = 17.945(7)A, and Z = 4, for a formula unit Cs(Mo0.95W0.05)7O21. The intensities (I) of 1431 reflections, for which I > 3σ(I), were considered observed. The structure was solved by direct and Fourier methods and refined by least squares to a value of 0.019 for the conventional R factor. It is based on the corner sharing of molybdenum coordination polyhedra, forming chains of five very distorted “octahedra” and two terminal tetrahedra. These chains, similar to those found in the structures of γ- and η-Mo4O11, pack to form a three-dimensional network, thus generating voids in which the Cs atoms are located with a coordination number of 12.

Dependence of the diffraction angle on the surface microstructure of a steel sample

While the deviations from linearity of e-sinZq, curves in the case of two welded hot-rolled C40 steel bars were being studied, this paper was prompted by the observation that, at q, = 0 °, the diffraction angle 20 depends on q~, the inclination angle of the diffraction plane with respect to an arbitrarily chosen reference plane attached to the specimen. This result is unexpected and cannot be explained by bulk structural or microstructural factors. A surface effect is offered as a possible explanation.

A Cluster Modelling Study of Conductivity of Yttria-Stabilized Zirconia

On the basis of a previously described structural model for the Yttria-Stabilized Zirconia, the conductivity for this material can be calculated. A fixed number of clusters is generated in a structure of 70×28 polyhedra to simulate different Y contents in the structure. The results are compared with the experimental results obtained by others and discussed.