Research Trends in Contemporary Materials Science

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Authors: L. Laversenne, Š. Miljanić, Philippe Miele, Christelle Goutaudier, B. Bonnetot
Abstract: High surface area nanoporous powders of hexagonal boron nitride (h-BN) have been prepared from molecular precursors to be used for hydrogen sequestration. The more promising samples were obtained using a precursor derived from trichloroborazine (TCB). The precursor was first reacted with ammonia at room temperature leading to the molecular complex Cl3B3N3H3, 6 NH3 which was heated up to 650 °C under ammonia and then up to 1000 °C under nitrogen, giving rise to a high reactive h-BN powder. This crude powder was stabilised by an annealing up to 1800 °C under nitrogen atmosphere leading to a very stable compound exhibiting a specific area of more than 300 m2·g-1 and presenting a very specific nanometric spherical texture. Some samples were doped with platinum (about 1 wt.%) to enhance the activity of pure h-BN using an original one step synthesis route starting from a mixture of BN and Pt precursors. Attempts to sequester hydrogen into these powders were made successfully at -196 °C under 10 MPa, but the stored amount was only about 0.3 wt.% and the platinum added BN powders did not lead to an enhancement of the storage capacity.
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Authors: Natalie V. Kamanina
Abstract: The fullerene-doping effect on spectral, nonlinear optical properties, and dynamic parameters of conjugated organic systems based on pyridine, polyimide, polyaniline, polyvinyl alcohol, liquid crystal, etc. has been studied. Introduction of fullerenes into these materials has been made due to their high electron affinity that allows intermolecular donor-acceptor interaction to be reinforced. The new charge transfer complex provokes new nanostructures potentials such as nonlinear transmission, laser-induced change in the refractive index, self-organization. The application of studied nanostructures in laser and display techniques, and medicine has been discussed.
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Authors: L. Pidol, Bruno Viana, Aurelie Bessière, A. Galtayries, P. Dorenbos, Bernard Ferrand
Abstract: The paper presents two cerium doped lutetium silicate crystals: pyrosilicate Ce:Lu2Si2O7 (LPS) and Ce: Lu2(1-x)Y2xSiO5 (LYSO). These two crystals exhibit the expected requirements for gamma detection: high density and high atomic number, high scintillation light yield, good energy resolution and fast response. LPS and LYSO crystals doped with cerium were grown by the Czochralski process. The crystal growth parameters were studied and optimized. Development of scintillators requires good understanding of the scintillation process. The location within the forbidden band gap of the localized lanthanide energy levels is analyzed by time resolved spectroscopy and thermoluminescence studies.
371
Authors: R. Krsmanović, Giovanni Bertoni, Gustaaf Van Tendeloo
Abstract: Samples of transparent glass-ceramics in the ternary system Li2O-Al2O3-SiO2 (LAS), with Er2O3 as a luminescent dopant, are investigated. The initial glass is obtained by the classical melting technique. In order to induce ceramization of the glass, TiO2 and ZrO2 are added in small amount as nucleating agents. The thermal treatments at 730 and 770°C are carried out to promote formation of titanium zirconate solid solution precipitates. The spatial distribution of the precipitates in the material, their morphology, and their composition are investigated with TEM, HRTEM, HAADF-STEM, EELS and EFTEM. The results demonstrate that with the glass-melting preparation technique it is possible to achieve small nanoparticles with uniform distribution and higher number density than with the sol-gel glass preparation.
377
Authors: Aurelie Bessière, Fabienne Pellé, Claire Mathieu, Bruno Viana, Philippe Vermaut
Abstract: Y2O3:19%Yb,1%Er nanoparticles were synthesized with the aim of imaging the luminescent cell. Coprecipitation and combustion synthesis were used to obtain particulate sizes ranging from 25 up to 140 nm. The powders showed predominant red upconversion and the emission efficiency is controlled by the particle size. A colloidal route was also followed and 2-5 nm-large agglomerated nanoparticles were obtained. In that case, the luminescence of Er3+ was only observed by direct excitation and no upconversion light has been detected on these very small particles.
383
Authors: B. Julián, J. Planelles, E. Cordoncillo, P. Escribano, C. Sanchez, P. Aschehoug, Bruno Viana, Fabienne Pellé
Abstract: In this work, Eu3+-doped CdS nanocrystals embedded in a SiO2 matrix were synthesised by a sol-gel method since this method confers a great chemical homogeneity, and allows in-situ generation and controlled growth of CdS nanocrystals within the silica glass. The influence of the sol-gel conditions on the Eu3+ optical response has been investigated. The synthesis conditions can be varied to modify the structure of the material, and the dispersion of the rare earth ion, within the silica matrix. From the optical analysis an energy transfer appears from CdS nanoparticles to Eu3+ ions but also a back transfer Eu3+ to CdS nanoparticles is evidenced.
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Authors: Ljiljana Kandić, K. Marinković, Lydia Mančić, G. del Rosario, O. Milošević
Abstract: The objective of this work is to present the results of the comparative analysis of YAG:Ce3+ microstructural parameters obtained from x-ray powder diffraction (XRPD) data using Rietveld based Koalariet and Fullprof programs. YAG:Ce3+ powder is obtained via low temperature aerosol route at 3200C followed by post annealing treatment. The chosen technique of synthesis, i.e. ultrasonic spray pyrolysis, provides the generation of spherically shaped and submicronically sized particles having composite nanostructure. Since the targeting garnet phase represents a very promising host phosphor material being doped with rare-earth ions, the most important criteria determining its applicability in various optical devices is the uniform distribution of the luminescent center in the host lattice as well as the cubic YAG phase crystallinity. Comparison of the data obtained for the same samples by the above mentioned XRPD analyses gives us an insight into the validity of the refined parameters.
395
Authors: Alex A. Kamanin, Natalie V. Kamanina
Abstract: Both the aligning effect of erythrocytes in nematic liquid crystal media and the phenomenon of induced rearrangement of pristine nematic liquid crystal have been observed. Reasons for structuralization of the nematic liquid crystal under the action of inserted nonelectrically- neutral biological components have been discussed. The observed effect is suggested to be quite general and consistent with previously obtained results for nematic liquid crystal under the action of fullerene-containing charge transfer complexes.
401
Authors: J. Jeknić, M. Dugić, D. Raković
Abstract: The complex behavior of microparticles in a solution calls for different theoretical backgrounds. Here, we follow the line of two, recently developed theories on individuality, on the one hand, and conformational transitions of macromolecules in a solution, on the other. Given as separate theories, the two models may raise certain controversy in respect to their mutual consistency. Needless to say, their mutual consistency is necessary for the validity of the theories both in a general context as well as in search for a unified physico/chemical picture concerning the microparticles in a solution dynamics. We point out the consistency of these theories based on the definition of a molecule through its constituent subsystems (e.g. the center-of-mass and the “conformation” subsystems).
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Authors: C. Gruenberger, R. Ritter, F. Aumayr, Herbert Stachelberger, Ille C. Gebeshuber
Abstract: Matter produced by organisms is remarkable. Evolutionary optimized properties, e.g. regarding hydrodynamic, aerodynamic, wetting and adhesive behavior, can already be found in the “simplest” forms of organisms. Euglena gracilis, a single-celled algal species, performs tasks as diverse as sensing the environment and reacting to it, converting and storing energy and metabolizing nutrients, living as a plant or an animal, depending on the environmental constraints. We developed a preparation method for atomic force microscopy investigation of dried whole Euglena cells in air and obtained data on whole cells as well as cell parts. Our studies corroborate TEM, SEM and optical microscopy results. Furthermore, we found new features on the pellicle, and set the ground for AFM force spectroscopy and viscoelastic studies on the nanoscale.
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