D.M. Trichês

The Use of Le Bail Method to Analyze the Semicrystalline Pattern of a Nanocomposite Based on Polyaniline Emeraldine-Salt Form and α-Al2O3

Ceramic nanocomposites constituted by a matrix of α-Al2O3 microparticles reinforced by polyaniline emeraldine-salt form (PANI-ES) nanoparticles were prepared by in situ polymerization and characterized structural and morphologically. Peaks related to both materials were observed through XRD technique: PANI-ES presented peaks at = 8.9, 14.9, 20.8, 25.3, 27.1, and 30.0° and in α-Al2O3 phase peaks were found at = 25.6, 35.2, 37.9, 43.5, 52.6, 57.6, and 68.1°. Nanocomposite crystallinity percentage was estimated around 70%. SEM showed a polymerization of PANI-ES over alumina plates. By Le Bail method it was observed that PANI-ES and α-Al2O3 have crystallite average size around, respectively, 41 and 250u2009A. By FTIR analysis characteristic absorption bands of both materials were identified. Additional bands indicating new chemical bonds were not observed, suggesting that nanocomposite was formed by physical deposition. Nanocomposite DC electrical conductivity was found around 0.24u2009S/cm (against u2009S/cm for pure PANI-ES), showing an increase of about 1,300 times compared to the pure PANI-ES at room temperature. Thus, this paper showed that both materials have kept its original structural characteristics and exhibited high electrical conductivity when combined in nanocomposite form.

Pressure‐induced polymorphism in nanostructured SnSe

The pressure-induced phase transitions in nanostructured SnSe were investigated using angle-dispersive X-ray diffraction in a synchrotron source along with first-principles density functional theory (DFT) calculations. The variation of the cell parameters along with enthalpy calculations for pressures up to 18u2005GPa have been considered. Both the experimental and the theoretical approaches demonstrate a phase transition at around 4u2005GPa. Below 8.2u2005GPa the X-ray diffraction patterns were fitted using the Rietveld method with space group Pnma (No. 62). The lattice parameters and atomic positions for the above-mentioned symmetry were used in DFT calculations of thermodynamic parameters. The enthalpy calculations with the computationally optimized structure and the proposed Pnma structure of SnSe were compatible. The variations of the cell volume for the high-pressure phases are described by a third-order Birch–Murnaghan equation of state.

Synthesis and properties of nanostructured GeSb 4 Te 7 prepared by mechanical alloying

A nanostructured GeSb4Te7 (GST147) phase was produced by mechanical alloying (MA), starting from a mixture with nominal GeSb2Te4 composition of high-purity elemental Ge, Sb and Te powders. The effect of milling on z-coordinates of Wyckoff sites 2c and 2d occupied by the Sb and Te atoms was studied using an approach combining the Rietveld method and pair distribution function analysis. The thermal stability of GST147 and the Raman active modes of GST147 were investigated. The results of photoacoustic absorption spectroscopy show that the thermal diffusivity of nanostructured GST147 produced by MA is similar that of its bulk counterpart.