Publications

High-density (92-98% of the theoretical density) MgB2 samples added with Sb2O5 ((MgB2)+ (Sb2O5) x, x = 0, 0.0025, 0.005, 0.015) were obtained by Spark Plasma Sintering. A higher amount of additive decreases density. In added samples, grains of secondary phases are located at MgB2 grain boundaries and they are of large size. Hence, Sb2O5 does not promote effective flux pinning, connectivity is lower, and this suppresses the critical current density and the irreversibility field. Pinning force-related parameters indicate that added samples are close to the point pinning region and they show a higher grain boundary pinning contribution when compared with pristine MgB2 sample and when temperature is lower. It is speculated that for fixed processing conditions and Sb-oxide phases, a lower stability of the additive, reflected by a lower melting temperature, may promote reactive processes to start earlier leading to coarsening of the grains belonging to secondary phases.

Facet 111 oriented Au nanoplatelets (20-40 nm wide, 3-4 nm height) grafted on graphene ((Au) over bar /fl-G) are about three orders of magnitude more efficient than Pd nanoparticles supported on graphene to promote Suzuki-Miyaura coupling. In contrast to Pd catalysis, it is shown here that the product yields in Suzuki-Miyaura coupling catalyzed by Au nanoparticles follow the order chlorobenzene > bromobenzene > iodobenzene. Kinetic studies show that this reactivity order is the result of the poisoning effect of halides for Au that is much higher for I- than Br- and much higher than for Cl-, due to adsorption. This strong iodide adsorption leading to Au catalyst deactivation was predicted by DFT calculations of Au clusters. (Au) over bar /fl-G are about one order of magnitude more efficient than small Au nanoparticles (4-6 nm) obtained by the polyol method supported on graphene. Our results can have impact in organic synthesis, showing the advantage of (Au) over bar /fl-G as catalyst for Suzuki-Miyaura couplings. (C) 2017 Elsevier Inc. All rights reserved.

Measurements of the magnetocapacitance effect in epitaxial La0.7Sr0.3MnO3/Pb(Zr0.2Ti0.8)O-3/La0.7Sr0.3MnO3 heterostructures have been performed using a quasi-static method. Through capacitance-voltage measurements carried out under variable magnetic field it has been found that the magneto-capacitance depends on the orientation of the ferroelectric polarization. The value of magneto-capacitance can be as high as 1% in the voltage range near the ferroelectric coercive field. This has been attributed to a variation of the apparent built-in voltage of the PZT-LSMO Schottky barriers on applied magnetic field.

Tunable reaction selectivity on a single catalyst is a continual goal in chemical syntheses. Herein, we report an unexpected light-directed intermediate selectivity using well-known plasmonic photocatalysts. We observed distinct intermediate selectivity behaviors between using UV and visible light irradiations. Chemical computations and quenching experiments suggest that the radicals generated by the plasmonic excitation govern the light-directed selectivity. The broader impact of this work ranges from selective yield of desirable intermediates for subsequent syntheses without tedious separation procedures, to arousing interest in examining new opportunities for plasmonic photocatalysts.

We investigate the down- and up-conversion properties of Er (0.3, 1 and 3%)-CeO2 and Er(1%)Yb(20%)-CeO2 nanoparticles by use of ns pulsed monochromatic excitation. The emission spectra were recorded in the visible to near-infrared range (500-1100 nm) under ultraviolet, visible (490 and 650 nm) and near infrared (790, 971/977 and 1470 nm) up-conversion excitations as well as X-ray excitation. The structural properties were characterized by X-ray diffraction, Raman, Diffuse Reflectance UV/Vis and Diffuse Reflectance Fourier Transform Infrared spectroscopies. The role of CeO2 charge transfer band as a level selective antenna sensitizer, the dopant induced oxygen vacancies and the effect of Er concentration on the overall emission properties are highlighted. The mechanisms involved in the up-conversion emission in Er-CeO2 and Er,Yb-CeO2 are analysed in terms of up-conversion excitation spectra, up-conversion emission decays and evolution of the red to green emission ratio with Er concentration and delay after the laser pulse. Our findings are also discussed in the context of a comprehensive literature survey regarding the actual stage of research on the luminescence of Er and Er,Yb doped CeO2 and their possible applications. (C) 2017 Elsevier B.V. All rights reserved.

A comparative study of morpho-structural, magnetic and magneto-transport properties of two Fe-Au granular films with different concentrations of Fe nanoclusters of almost similar size is reported. Different organizations of the Fe clusters, i.e. in lamellar-like or random-like configuration, were obtained by varying the amount of Fe in the Fe-Au films. The specific magnetic behaviour was investigated with respect to local structure and morpho-structural aspects by combining magneto-optic Kerr effect and superconducting quantum interference device magnetometry, Fe-57 conversion electron Mossbauer spectroscopy and a wide range of electron microscopy techniques. A strong in-plane magnetic texture with uniaxial anisotropy was observed in the case of the lamellar-like organization of the clusters (specific to the Fe-Au film with higher Fe concentration) whereas a superparamagnetic behaviour was evidenced in the case of random distribution of the clusters (specific to the Fe-Au film with lower Fe concentration), despite the similar average size of the clusters in the two samples. Specific magnetoresistance effects were investigated with respect to both the involved magnetic configurations and magnetic interactions of the Fe clusters.

The synthesis and physicochemical characterization of riboflavin (RF) loaded Myrj52-silver nanoparticles (SNPs) were performed and their cytotoxic properties were evaluated. Transmission electron microscopy analysis showed the formation of colloidal spherical SNPs with an average size of similar to 12 nm. The structure, stability, dynamics and conformation of human serum albumin (HSA) binding RF on SNPs have been studied. The influence of RF on the secondary structure of HSA in the presence of SNPs showed a predominant alpha-helix structure (61.7%). No changes induced by RF binding to HSA were observed. The cytotoxicity of RF and RF-HSA loaded Myrj52-SNPs was evaluated in vitro using the Neutral Red assay and cell morphology observations in a culture of L929 fibroblast cells. The results have relevance with regard to the RF loaded Myrj52-SNP formulation for pharmaceuticals.

Local symmetry distortion by Li addition is acknowledged as an effective strategy for enhancing the luminescence of lanthanide (Ln) doped into a wide range of lattice hosts. Despite extensive literature, direct evidence that supports Li-induced modification of the local crystal-field at the Ln sites is still missing. Herein, we show that the emission enhancement by Li addition in Ln,Li-Y2O3 is due to improved crystallization and not to local structure distortion. Our approach is based on the premise that any distortion/lowering of the local symmetry would reflect into the alteration of the emission shapes and shortening of the emission decays. To this aim, we have extensively investigated the evolution with Li addition and calcination temperature of down (optical and X-ray induced) and up-conversion (UPC) emission of Ln-Y2O3 measured across the visible to near-infrared range. First, a center to center (corresponding to Ln in the C-2 and S-6/C-3i sites of the cubic Y2O3 lattice) as well as global comparison of the emission properties of Li free and Li codoped Y2O3 are presented by use of Eu, Sm, Tb and Dy as local probes in the visible range. Next, the effect of Li on the up-conversion emission of Er-Y2O3 is analyzed in terms of UPC pathways, emission shape and intensity, decays and excitation spectra. It is concluded that Li addition does not change either the local structure around C-2 or S-6 Ln centers or the relative contribution of these. Moreover, it is found that the effects of Li doping on the emission properties of Ln-Y2O3 are like extending the calcination temperature of Li-free Ln-Y2O3 from 800 degrees C to similar to 1000-1100 degrees C. Additionally, a relatively intense 1500 to 980 nm UPC emission is evidenced for the first time for Er-Y2O3, while a relatively intense "emission around 1500 nm was measured under X-ray excitation. Taken together, our findings highlight the need for revisiting the traditional optimization strategy based on Li modification but also the promise of Er-Y2O3 nanoparticles for optical/X-ray applications in the near-infrared range.

The structural electronic and magnetic properties of CoFeZrSi material with tetragonal and triclinic distorted primitive cell were investigated within the Density Functional Theory (DFT) framework. Half metallic soft ferromagnetism with high Curie temperature was evidenced in this quaternary compound which crystallizes optimally in the cubic LiMgPdSn type structure. The material preserves the half metallic characteristic when the cubic primitive cell is tetragonally deformed or when the unit cell volume increases or decreases due to external applied pressure. On contrary, the energy band gap, typical for half-metals, located in the minority spin channel disappears when the unit cell is triclinic deformed, e.g. under interfacial distortions. The material exhibits metallic behavior and the total magnetic moment increases from the integral 1 mu B/f.u., calculated for cubic and tetragonal unit cells, up to 3.25 mu B/f.u. for triclinic structure with a = b = c and alpha = beta = 90 degrees gamma = 89 degrees. (C) 2017 Elsevier B.V. All rights reserved.

Nano-sized lanthanum doped barium titanate Ba1-xLaxTiO3 (0.00 <= x <= 0.08) powders were prepared by sol-gel method. These powders with perovskite BaTiO3 cubic single phase structure, obtained after calcinations of gels precursors at 1100 degrees C, 3 h in air, were pressed and sintered by spark plasma technique in order to obtain dense ceramics. The optimal sintering temperatures used for Ba1-xLaxTiO3 powders were dependent on lanthanum amount added to barium titanate and decrease from 1300 degrees C to 1160 degrees C when the La concentration increases from 0 to 8 at.% La. An additional annealing treatment was made in air at 900 degrees C for all the sintered pellets for oxidize and remove the contaminant graphite which migrated in ceramics from the graphite die during the sintering process. The effect of lanthanum concentration on the densification behavior, structure, microstructure, photoluminescence and dielectric properties of the Ba1-xLaxTiO3 ceramics was investigated in this work. The results shown that as the lanthanum content increases, the grain size of the powders and ceramics increases accompanied by decrease of density of the samples. Also, increase of La amount inserted in BaTiO3 lattice leads to significant decrease of the dielectric losses and Curie temperature and, increase of dielectric permittivity but the luminescence properties seem to be less affected. (C) 2017 Elsevier B. V. All rights reserved.