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Deganello F.,CNR Institute of Nanostructured Materials | Testa M.L.,CNR Institute of Nanostructured Materials | La Parola V.,CNR Institute of Nanostructured Materials | Longo A.,CNR Institute of Nanostructured Materials | And 2 more authors.
Journal of Materials Chemistry A

A combined soft-hard templating (SHT) approach was used to prepare LaFeO3-based perovskite nanopowders with high surface area and porosity. In the SHT approach, a self-sustained combustion process between a soft fuel (citric acid) and an oxidant (metal nitrates) occurs in the presence of a silica hard template (amorphous, HMS or SBA-15 silica). The as-burned powders were then calcined, processed by basic etching and carefully characterized by X-ray diffraction combined with Rietveld refinement, small angle X-ray scattering, neutron activation analysis, N2-adsorption, X-ray photoelectron spectroscopy and transmission electron microscopy. It was observed that structural, microstructural and textural properties of the obtained nanopowders strongly depend on the hard template used and an excellent correlation was found between the samples' specific surface area and cumulative pore volume of the original hard template. The use of several complementary characterization techniques revealed the composite nature of the prepared materials, evidencing the presence of amorphous La and Fe silicates in all the LaFeO3 nanopowders. Furthermore, it was demonstrated that these silicates have an important function in the transmission of the microstructural-morphological-textural features from the template to the final powder. © 2014 the Partner Organisations. Source

Sciortino L.,University of Palermo | Giannici F.,University of Palermo | Martorana A.,University of Palermo | Ruggirello A.M.,University of Palermo | And 4 more authors.
Journal of Physical Chemistry C

Cobalt-nickel bimetallic nanoparticles were synthesized by changing the sequence of the chemical reduction of Co(II) and Ni(II) ions confined in the core of bis(2-ethylhexyl)phosphate 2, and Ni(DEHP) 2. The reduction was carried out by mixing, sequentially or contemporaneously, fixed amounts of n-heptane solution of Co(DEHP) 2 and Ni(DEHP) 2 micelles with a solution of sodium borohydride in ethanol at a fixed (reductant)/(total metal) molar ratio. This procedure involves the rapid formation of surfactant-coated nanoparticles, indicated as Co/Ni (Co after Ni), Ni/Co (Ni after Co), and Co + Ni (simultaneous), followed by their slow separation as nanostructures embedded in a sodium bis(2-ethylhexyl)phosphate matrix. The resulting composites, together with those obtained by reducing the n-heptane solutions of pure Co(DEHP) 2 or Ni(DEHP) 2, were characterized by XPS, EXAFS, WAXS, and SAXS. The data analysis confirms the presence of nanometer-sized surfactant-coated cobalt, nickel, and cobalt/nickel particles. As expected, the composition and internal structure of cobalt/nickel bimetallic nanoparticles are influenced by the preparation sequence as well as by the "chemical affinity" between the surfactant and the metal. However, some atomic-scale physicochemical processes play a subtle role in determining the structural features of bimetallic nanoparticles. Further effects due to the competition between nanoparticle growing process and surfactant adsorption at the nanoparticle surface were observed. © 2011 American Chemical Society. Source

Li D.Y.,Catholic University of Leuven | Zeng Y.J.,Catholic University of Leuven | Batuk D.,University of Antwerp | Pereira L.M.C.,Catholic University of Leuven | And 10 more authors.
ACS Applied Materials and Interfaces

ZnO-Co nanocomposite thin films are synthesized by combination of pulsed laser deposition of ZnO and Co ion implantation. Both superparamagnetism and relaxor ferroelectricity as well as magnetoelectric coupling in the nanocomposites have been demonstrated. The unexpected relaxor ferroelectricity is believed to be the result of the local lattice distortion induced by the incorporation of the Co nanoparticles. Magnetoelectric coupling can be attributed to the interaction between the electric dipole moments and the magnetic moments, which are both induced by the incorporation of Co. The introduced ZnO-Co nanocomposite thin films are different from conventional strain-mediated multiferroic composites. © 2014 American Chemical Society. Source

Longo A.,CNR Institute of Nanostructured Materials | Longo A.,Netherlands Organization for Scientific Research NWO | Sciortino L.,University of Palermo | Giannici F.,University of Palermo | Martorana A.,University of Palermo
Journal of Applied Crystallography

The properties of nanostructured cobalt in the fields of magnetic, catalytic and biomaterials depend critically on Co close packing. This paper reports a structural analysis of nanosized cobalt based on the whole X-ray diffraction (XRD) pattern simulation allowed by the Debye equation. The underlying structural model involves statistical sequences of cobalt layers and produces simulated XRD powder patterns bearing the concurrent signatures of hexagonal and cubic close packing (h.c.p. and f.c.c.). Shape, size distribution and distance distribution between pairs of atoms are also modelled. The simulation algorithm allows straightforward fitting to experimental data and hence the quantitative assessment of the model parameters. Analysis of two samples having, respectively, h.c.p. and f.c.c. appearance is reported. Extended X-ray absorption fine-structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra are simulated on the basis of the model, giving a tool for the interpretation of structural data complementary to XRD. The outlined structural analysis provides a rigorous structural basis for correlations with magnetic and catalytic properties and an experimental reference for ab initio modelling of these properties. © 2014 International Union of Crystallography. Source

Lieten R.R.,Catholic University of Leuven | Lieten R.R.,IMEC | Lieten R.R.,Entegris | Fleischmann C.,IMEC | And 12 more authors.
ECS Journal of Solid State Science and Technology

We have investigated the structural and optical properties of metastable amorphous and crystalline GeSn layers on Si substrates. The as-deposited amorphous layers crystallize during annealing at 500°C. This transition leads to a significant change in the local environment of the Sn atoms and in the optical properties. The Ge-Sn bond length is decreased after crystallization. The as-deposited GeSn layers, with nominal 4.5% and 11.3% Sn content, do not show Sn segregation. For the crystallized GeSn with nominal 4.5%, the Sn appears to be substitutional, as no Sn clustering was observed. However, for the crystallized GeSn with nominal 11.3% Sn, Sn segration and the presence of β-Sn is observed by EXAFS. A method to suppress Sn segregation and increase the substitutional Sn concentration is discussed. Furthermore, we determined the optical properties of amorphous and crystalline GeSn with nominal 4.5% Sn. The bandgap energy decreases significantly from 0.89 eV (1392 nm) ± 0.05 eV for the amorphous layer to 0.52 eV (2383 nm) ± 0.05 eV for crystalline GeSn, leading to significant reduction in penetration depth. © The Author(s) 2014. All rights reserved. Source

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