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[EN] Dense multiferroic 0-3 type composites encompassing BaTiO and YFeO were fabricated by the solid-state reaction method. X-ray diffraction data combined with scanning electron microscopy imaging show virtual immiscibility between the two phases, with the YFeO ferrimagnetic phase well dispersed in the tetragonal BaTiO ferroelectric matrix. Raman spectroscopy analyses corroborate the polar nature of the BaTiO matrix in composites with a YFeO content as great as 40 wt%. Ferrimagnetism is detected in all composites and no additional magnetic phases are distinguished. Although these dense ceramics can be electrically poled, they exhibit a very weak magnetoelectric response, which slightly increases with YFeO content., This work was funded by the Christian Doppler Association in cooperation with TDK-EPC (Austria). LM acknowledges the grant PN-II-ID-PCE-2011-3-0745, while MA thanks funding by Spanish MINECO through project MAT2014-58816-R.

This work presents a solvent-free and laser-assisted growth of gold nanoparticles (Au-NPs) within silica monoliths using both Au(III) and Au(I) precursors. The novelty of the synthesis method is that Au-NPs of about 20 nm in diameter were obtained well dispersed in the matrix with no need of either reducing or capping agents. Moreover, the laser-assisted synthetic procedure here described made it possible to obtain reproducible 2D and 3D patterns of Au-NPs. For this purpose, suitable Au(I) and Au(III) precursors, soluble in dichloromethane, were easily prepared following a well-known procedure. The mesoporous silica matrix was first loaded with the precursors via a simple impregnation and then irradiated using either a continuous laser (?= 266 or 532 nm) or a pulsed laser (?=800 nm; pulse: 120 fs; repetition rate: 1KHz). In all cases, a photothermal gold reduction was observed. The Au-NPs have been characterized using UV-vis absorption spectroscopy, x-ray diffraction and Transmission Electron Microscopy. Finally it is shown that the excess gold precursors can be removed after the Au-NP synthesis by a simple washing of the monolith with a few immersions in the pure solvent. The stability of the Au-NPs was further tested by a series of heat-treatments up to 500°C, showing that the silica monolith acts as an effective support to prevent the agglomeration of the nanoparticles. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

International audience; Platinum nanoparticles supported on nanostructured cellulose-based carbon aerogels (carbonized aerocellulose, CAC) were evaluated in proton exchange membrane fuel cell (PEMFC). The CAC substrate was synthesized through the dissolution, gelation, regeneration, supercritical CO2 drying and pyrolysis of cellulose. The Pt nanoparticles deposition was performed by impregnation of the CAC with H2PtCl6, followed by Pt z species reduction either under H2 at 300-400C or in basic NaBH4 solution. While H2 reduction leads to uniform Pt nanoparticles well-dispersed over the CAC surface, larger agglomerates form with NaBH4 reduction, as revealed by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD). The reduction methods influences the quantity of platinum deposited, which may be increased by using multiple impregnation/reduction steps. The specific surface area of Pt and specific/mass activities towards oxygen reduction of the Pt/CAC materials, investigated using the rotating disk electrode setup, are similar to those of commercial Pt/Carbon Black (CB). Finally, PEMFC unit cell testing demonstrates that a Pt/CAC sample synthesized using three successive impregnation/reduction steps, loaded at ca. 14 wt Pt/(Pt C), competes with state-of-the-art Pt/CB electrocatalysts of comparable Pt loading

cited By 16; International audience; Well-dispersed nano-crystalline transition alumina suspensions were mixed with yttrium chloride aqueous solutions, with the aim of producing Al2O3-Y3Al5O12 (YAG) composite powders. DTA analysis allowed to highlight the role of yttrium on the α-phase crystallization path. Systematic XRD and HRTEM analyses were carried out in parallel on powders calcined in a wide temperature range (600-1300°C) in order to follow phase and microstructural evolution. A thin, homogeneous yttrium-rich layer was yielded on the alumina particles surface; yttrium diffusion into the alumina matrix was negligible up to 1150°C whereas, starting from 1200°C, aggregates of partially sintered alumina particles appeared, stuck together by yttrium-rich thin films. Moreover, in the yttrium-richer zones, such as alumina grain boundaries and triple joints, yttrium-aluminates precipitated at alumina particles surface. Finally, at 1300°C, alumina-YAG composite powders were produced, in which YAG was homogenously distributed among the alumina grains. © 2010 Elsevier Ltd.