Publications

Superconducting bulks of MgB2 with addition of Sb2O3 and Sb with different stoichiometric compositions ((MgB2) + (Sb2O3) (x) , x = 0.0025, 0.005, 0.015, and (MgB2) + (Sb)(y), y = 0.01) were obtained by the Spark Plasma Sintering (SPS) technique. All added samples have high density, above 95% and critical temperature, T (c), of 38.1-38.6 K. This result and XRD data suggest that Sb does not enter the lattice of MgB2. Impurity phases are Mg3Sb2, MgO, and MgB4. The optimum addition is Sb2O3 for x = 0.005. This sample shows the critical current density, J (c)(5 K, 0 T) = 4 x 10(5) A/cm(2) and J (c)(5 K, 7 T) = 6 x 10(2) A/cm(2), while the irreversibility field, H (irr) (5 K, 100 A/cm(2)) = 8.23 T. Indicated values of J (c) and H (irr) are higher than for the pristine sample. The mechanism of J (c) and H (irr) increase in the Sb2O3 added samples is complex and composed of opposite effects most probably involving morphology elements, the presence of nano metric MgB4 and the indirect influence of oxygen or oxygen and Sb. Crystallite size of MgB2 is decreasing when Sb-based additions are introduced and the effect is stronger for the Sb-metal addition. The sample with Sb-metal addition does not improve J (c) and H (irr) when compared with pristine sample.

We report an original way to prepare luminescent glass-ceramic microrods containing Eu3+ doped BaF2 nanocrystals by sol-gel chemistry within the pores of a polycarbonate template membrane. Structural characterization by scanning electron microscopy and X-ray diffraction has shown the formation of glass-ceramic microrods with 0.8-m diameter of and 10 mu m length in which BaF2 nanocrystals of about 30 nm size are embedded. Photoluminescence measurements have indicated the incorporation of Eu3+ ions inside the BaF2 nanocrystals in a broad range of sites with low coordination symmetry. The comparison made with the bulk glass-ceramic indicated an influence of the dimensional constraints imposed by the membrane pores during xerogel formation and subsequent glass ceramization.

(Bi0.5Na0.5)TiO3 doped with 8 mol% BaTiO3 powder prepared by sol-gel was compacted and sintered by spark-plasma-sintering method. The influence of spark-plasma-sintering temperature on the densification and piezoelectric properties of these ceramics was studied. Starting from BNT-BT0.08 powder gel with a microstructure consisting of particles with average size of 50 nm, ceramics with grain size of 60-90 nm and density of about 98.9-99.6% of the theoretical density were obtained by spark-plasma-sintering at 800-900 A degrees C. Increasing the sintering temperature by SPS from 800 to 900 A degrees C lead to the increase of d (33), k (p), epsilon (33) (T) and, decrease of Q (m). Typical d (33) and k (p) values of BNT-BT0.08 ceramics sintered by spark-plasma-sintering at 900 A degrees C were 8 and 0.029, respectively.

Photoluminescence and magnetic circular dichroism of the IrQ(ppy)(2)-5Cl compound were investigated between 15 and 295 K. These results have been compared with the output files obtained from Density Functional Theory by using the Gaussian 03W software and some additional packages. The experimental results confirm the first triplet state absorption which arises from d to pi(Q) transition. The temperature dependence photoluminescence have shown a small interaction with the polystyrene, used for dispersion of IrQ(ppy)(2)-5Cl compound. The green and red phosphorescence have the same temperature dependence. The MCD spectra, especially at 15K, reveals the main transitions involved in the Metal-to-Ligand Charge Transfer processes from the Ir towards the two ligands, phenylpyridine and quinoline, respectively. (C) 2011 Elsevier B.V. All rights reserved.

Te metal or TeO2 were added to MgB2 ((MgB2) (A)(x), x = 0.005, 0.01, 0.03, A = addition). The mixtures were processed by spark plasma sintering. The critical current density J(c), of the samples containing the Te/TeO2 additions is enhanced at high fields and at temperatures up to 20K. The curve of J(c)(5 K, H) for the sample with optimum x(Te) = 0.01 shows no accelerated decrease up to 8 T (J(c)(5 K, 8 T) = 1.8 x 10(3) A cm(-2)). The irreversibility field of the samples containing the Te/TeO2 additions is also enhanced. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Carbon nanowalls (CNWs) functionalization allows the tailoring of some of their properties after they have been synthesized. Herewith we report on post-synthesis CNWs functionalization by plasma treatments. Radiofrequency plasmas generated in hydrogen, oxygen, nitrogen, tetrafluoroethane, and sulfur hexafluoride admixed to argon, were used. The changes of morphology, structure, chemical composition were determined by SEM, FTIR, Raman Spectroscopy, specifically for each gas mixture. The results point out to the surface erosion, the functional groups attachment, or to thin film coverage of CNWs material. Such processes strongly influence the material properties, as exemplified by the wettability: superhydrophilic or superhydrophobic surfaces are obtained starting from the same base CNWs material.

The Bose glass theory for the vortex matter in superconductors with correlated disorder predicts the depinning of vortices due to the renormalization of the pinning barriers by thermal fluctuations. In the case of YB2Cu3O7 theoretical estimates give a depinning temperature T-dp very close to the critical temperature T-c (T-dp similar to 0.95T(c)), while the results of standard magnetization relaxation experiments are repeatedly interpreted in terms of a much lower T-dp (similar to 0.5T(c)). We determined the temperature T variation of the normalized magnetization relaxation rate S for YB2Cu3O7 films containing BaZrO3 nanorods preferentially oriented along the c axis, with the external magnetic field applied along the nanorods. By extending the T interval up close to Tc, below the matching field a rich nonmonotonous S(T) variation was observed. It is shown here that the often analyzed S(T) maximum occurring at relatively low T (which was connected to a disappointing T-dp) has an extrinsic origin, related to thermomagnetic instabilities. The accommodation of vortices to the columnar pins in the presence of the T -dependent macroscopic currents induced in the sample during experiments is actually signaled by a pronounced S(T) deep located at high T, indicating that T-dp remains close to T-c, in agreement with the theoretical prediction.

The phase of the electronic wave function is not directly measurable but, quite remarkably, it becomes accessible in pairs of isospectral shapes, as recently proposed in the experiment by Moon et al. [Science 319, 782 (2008)]. The method is based on a special property, called transplantation, which relates the eigenfunctions of the isospectral pairs, and allows us to extract the phase distributions, if the amplitude distributions are known. We numerically simulate such a phase extraction procedure in the presence of disorder, which is introduced both as Anderson disorder and as roughness at edges. With disorder, the transplantation can no longer lead to a perfect fit of the wave functions, however we show that a phase can still be extracted-defined as the phase that minimizes the misfit. Interestingly, this extracted phase coincides with (or differs negligibly from) the phase of the disorder-free system, up to a certain disorder amplitude, and a misfit of the wave functions as high as similar to 5%, proving a robustness of the phase extraction method against disorder. However, if the disorder is increased further, the extracted phase shows a puzzle structure, no longer correlated with the phase of the disorder-free system. A discrete model is used, which is the natural approach for disorder analysis. We provide a proof that discretization preserves isospectrality and the transplantation can be adapted to the discrete systems.

Background: In this work the chemical structure of dextran-iron oxide thin films was reported. The films were obtained by MAPLE technique from composite targets containing 10 wt. % dextran with 1 and 5 wt.% iron oxide nanoparticles (IONPs). The IONPs were synthesized by co-precipitation method. A KrF* excimer laser source (lambda = 248 nm, tau(FWHM)congruent to 25 ns, nu = 10 Hz) was used for the growth of the hybrid, iron oxide NPs-dextran thin films. Results: Dextran coated iron oxide nanoparticles thin films were indexed into the spinel cubic lattice with a lattice parameter of 8.36 angstrom. The particle sized calculated was estimated at around 7.7 nm. The XPS shows that the binding energy of the Fe 2p(3/2) of two thin films of dextran coated iron oxide is consistent with Fe3+ oxides. The atomic percentage of the C, O and Fe are 66.71, 32.76 and 0.53 for the films deposited from composite targets containing 1 wt.% maghemite and 64.36, 33.92 and 1.72 respectively for the films deposited from composite targets containing 5 wt.% maghemite. In the case of cells cultivated on dextran coated 5% maghemite gamma-Fe2O3, the number of cells and the level of F-actin were lower compared to the other two types of thin films and control. Conclusions: The dextran-iron oxide continuous thin films obtained by MAPLE technique from composite targets containing 10 wt.% dextran as well as 1 and 5 wt.% iron oxide nanoparticles synthesized by co-precipitation method presented granular surface morphology. Our data proved a good viability of Hep G2 cells grown on dextran coated maghemite thin films. Also, no changes in cells morphology were noticed under phase contrast microscopy. The data strongly suggest the potential use of iron oxide-dextran nanocomposites as a potential marker for biomedical applications.

Iron oxide oxide nanoparticles were prepared by chemical co-precipitation method. The nanoparticles were mixed with dextran in distilled water. The obtained solutions were frozen in liquid nitrogen and used as targets during matrix assisted pulsed laser evaporation for the growth of hybrid, iron oxide nanoparticles-dextran thin films. Fourier Transform Infrared Spectroscopy and X-ray diffraction investigations revealed that the obtained films preserve the structure and composition of the initial, non-irradiated iron oxide-dextran composite material. The biocompatibility of the iron oxide-dextran thin films was demonstrated by 3-(4.5 dimethylthiazol-2yl)-2.5-diphenyltetrazolium bromide-based colorimetric assay, using human liver hepatocellular carcinoma cells. (C) 2011 Elsevier B.V. All rights reserved.