National Institute Of Materials Physics - Romania
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articles found
4461. Structural and magnetic properties of polypyrrole nanocomposites
Authors:
Turcu, R; Peter, I; Pana, O; Giurgiu, L; Aldea, N; Barz, B; Grecu, MN; Coldea, A
Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 417, 727, DOI: 10.1080/15421400490478939
We report the synthesis and characterization of conducting polymer nanocomposites based on polypyrrole (PPY) and Fe2O3 magnetic particles. The global structure of PPY nanocomposites was obtained by X-ray Diffraction (XRD) method using a new approximation based on Generalized Fermi Function. The local structural parameters of Fe sites in Fe2O3 nanocrystallites embedded in PPY were determined by X-ray Absorption Spectroscopy (EXAFS). The lack of hysteresis loop for the magnetization curves of the composite PPY-Fe2O3 indicates a superparamagnetic behavior which is typical for nanosized magnetic particles.
4462. Microstructure of Si/Sio(2) nanocomposite films
Authors:
Teodorescu, VS; Ciurea, ML; Iancu, V; Blanchin, MG
Published: 2004, 2004 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1AND 2, PROCEEDINGS, 62, DOI: 10.1109/SMICND.2004.1402802
The paper presents the inicrostructure of the Si/SiO2 nanocomposite films prepared by co-sputtering from Si and SiO2 targets. High resolution transmission electron microscopy and electron diffraction were used to reveal and compare the structures with different silicon/oxygen (SiOx, 0 < x < 2) coinposition. Si nanocrystallites have been evidenced clearly in the SiO1.6 areas. Percolation limits between the Si crystallites was observed in the x=1 areas. The morphology of the Si nanocrystallites and the amorphous SiO2 zones were compared in regions with different composition.
4463. Confining effects in composites containing molecular sieves
Authors:
Frunza, L; Frunza, S; Enache, I; Beica, T; Schonhals, A; Kosslick, H; Bentrup, U; Pitsch, I
Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 418, 813, DOI: 10.1080/15421400490479145
Confinement of 4n-octyl-4'-cyanobiphenyl to nanoporous molecular sieves with hexagonal structure of cylindrical pores or with cellular structure is studied. It was found by differential scanning calorimetry and broadband dielectric spectroscopy that composites with the pores completely filled with liquid crystal show phase transitions characteristic for bulk, while the partially filled samples do not show these transitions. Thermogravimetric, differential thermal analysis and in situ infrared spectroscopic investigations have indicated first time that the dealkylation and oxidation of the confined liquid crystal is quite possible inside the nanopores of these molecular sieves, at temperatures much lower than for the bulk.
4464. Epoxidation of cyclohexene on silicalite embedded BiOx clusters
Authors:
Parvulescu, VI; Florea, M; Gelbard, G; Centeno, MA; Macovei, D; Lemay, G; Kaliaguine, S
Published: 2004, RECENT ADVANCES IN THE SCIENCE AND TECHNOLOGY OF ZEOLITES AND RELATED MATERIALS, PTS A - C, 154, 2654, DOI:
Silicalite embedded BiOx Clusters were prepared both with and without Na using sodium silicate and tetraethylorthosilicate as silicium precursors. Catalysts with 3 and 5 wt% Bi were obtained. The MFl structure was established from XRD, TEM, and N-2 adsorption measurements. No deterioration of the silicalite framework by bismuth was observed. Bi exists as BiOx clusters as evidenced from XPS and EXAFS characterization. These clusters are localized inside the silicalite channels. Py-FTIR measurements indicated that 5wt% Bi led to the formation of strong Lewis acid sites. Epoxidation of cyclohexene was found to depend oil both Bi and Na content. On 3%Bi-ZSM-5 it occurred with rather good conversion and selectivity to epoxide. No visible leaching was evidenced. The catalysts were reused for several runs.
4465. C-60 aggregates in pyrrolidine and N-methyl-2-pyrrolidinone evidenced by surface-enhanced Raman scaterring spectra
Authors:
Baibarac, M; Preda, N; Mihut, L; Velula, T; Baltog, I; Mevellec, JY; Lefrant, S
Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 417, 587, DOI: 10.1080/15421400490478434
At room temperature, soluted C-60 in pyrrolidine and N-methyl-2-pyrrolidinone associates slowly in stable aggregates. The process originates in the charge transfer from the solvent molecules as electron donors towards fullerene. In the aggregate phase the intermolecular interactions lead to a large reduction in parent I-h C-60 symmetry such that a modified phonon spectrum is observed. Using the surface-enhanced Raman scattering we demonstrate that the Raman range below 800 cm(-1) is most diagnostic for aggregate assignment. In particular, the strong decrease of the radial breathing mode and appearance of new bands at 110 and 93 cm(-1) due to the interball interactions must be noticed.
4466. Sers spectra of polyaniline/carbon nanotubes and polyaniline/fullerene composites
Authors:
Baibarac, M; Baltog, I; Lefrant, S; Mevellec, JY; Chauvet, O
Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 415, 155, DOI: 10.1080/15421400490481269
SERS and FTIR spectra of M and S composites, provided by adding of single-walled carbon nanotubes (SWNTs) to the polyaniline (PANI) solution and chemical polymerization of aniline, respectively are different. The difference originates in the irreversible transformation of SWNTs in the polymerization medium. This explains the similarity of SERS and FTIR spectra of PANI/SWNTs and PANI/C-60 composites, chemically synthesized. For M composites, strong hindrance effects are evidenced by band at 773-755 cm(-1) associated to the vibration of deformation of the benzene and quinoid ring. The charge transfer is illustrated for all compounds by absorption band at 1144 cm(-1).
4467. Growth and properties of Pb(Zr0.92Ti0.08)O-3 thin films
Authors:
Boerasu, I; Pintilie, L; Gomes, MJM; Pereira, M
Published: 2004, INTEGRATED FERROELECTRICS, 62, 87, DOI: 10.1080/10584580490460556
Lead zirconate-titanate (PZT) thin films with Zr/Ti ratio of 92/8 were deposited by sol-gel on Pt(111)-coated Si(100) and single crystal MgO(100) substrates. The films crystallize differently on the two type of substrates: in case of the films deposited on Pt the perovskite structure is established only after oxygen annealing, while for the films deposited on MgO annealing in air is enough. The films are polycrystalline with some preferred orientation that is substrate dependent. Average values of 2.1 muC/cm(2) and 78 kV/cm were obtained for remnant polarization and coercive field, respectively. The I-V characteristic at low to medium voltages is dominated by field enhanced Schottky emission, with Ln(J)similar to(V + V-bi)(1/4) dependence of the current density. A value of about 3.85 eV was estimated for the band-gap from optical measurements.
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