Publications

Nanoparticle system with the composition xEu(2)O(3)-(1-x)alpha-Fe2O3 (x = 0.1 and 0.5) was successfully synthesized by mechanochemical activation of Eu2O3 and alpha-Fe2O3 mixtures for 0-12 hours of ball milling time. The study is of relevance to catalysis, biomedical, sensing and energy-related applications. Fe-57 and Eu-151 Mossbauer spectroscopy were used to investigate the phase evolution, solid solution formation and hyperfine parameters of xEu(2)O(3)-(1-x)alpha-Fe2O3 nanoparticle system under the mechanochemical activation process. The Fe-57 Mossbauer studies showed that the spectrum of the ball milled samples evolved from a sextet for hematite to sextets and a doublet upon duration of the milling process with europium oxide. This indicated the formation of the EuFeO3 perovskite for large x values and long milling times. The Eu-151 Mossbauer investigations showed that the isomer shift decreased with increasing milling time for all molar concentrations employed.

Restoration of damaged bone tissue involves two traditional approaches: tissue grafting and alloplastic replacement. Recently, their limitations led to the development of tissue engineering, which uses degradable porous supports named "scaffolds". These porous structures (used both for tissue engineering and classic bone substitution applications) with customizable designs may be constructed by solid freeform fabrication (SFF) techniques. SFF uses various synthetic materials and may be adapted for creating ceramic-based scaffolds, which became popular due to increased demands for bone substitution materials. Among these materials, naturally derived ceramics are suitable candidates for bone replacement due to their resemblance with the mineral bone. Innovative optimization routes for preparing naturally derived ceramics with modulated properties implies the management of key parameters involved in heat treatment of animal hard tissues: temperature, heating environment, and cooling conditions. Both powders and bulk pieces are evaluated with complementary techniques that focus on compositional, morphological, and structural features. Finally, qualitative and quantitative biological assay in relevant cell culture of the compacted powders may assist extensive testing programs for further evaluation of different ceramic scaffolds. All these results contribute to effective assessment of ceramics tuning strategies and to subsequent modulation of their enhanced properties and long-term functionality.

In this paper, we report the structural and morphological properties of silver-doped hydroxyapatite (AgHAp) with a silver concentration x(Ag) = 0.5 before and after being thermal treated at 600 and 1000 degrees C. The results obtained by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy suggest that the structure of the samples changes gradually, from hydroxyapatite (AgHAp_40) to a predominant beta-TCP structure (AgHAp_1000), achieved when the thermal treatment temperature is 1000 degrees C. In the AgHAp_600 sample, the presence of two phases, HAp and beta-TCP, was highlighted. Also, scanning electron microscopy studies suggest that the shape and dimension of the nanoparticles begin to change when the temperature increases. The antimicrobial activity of the obtained compounds was evaluated against Klebsiella pneumoniae, Staphylococcus aureus, and Candida albicans strains.

The effects of the bonding mechanism and band alignment in a ferroelectric (FE) BaTiO3/ferromagnetic La0.6Sr0.4MnO3 heterostructure are studied using x-ray photoelectron spectroscopy and first-principles calculations. The band lineup at the interface is determined by a combination of band bending and polarization-induced modification of core-hole screening. A Schottky barrier height for electrons of 1.22 +/- 0.17 eV is obtained in the case of downwards FE polarization of the top layer. The symmetry of the bonding states is emphasized by integrating the local density of states +/- 0.2 eV around the Fermi level, and strong dependence on the FE polarization is found: upwards, polarization stabilizes Ti t(2g) (xy) orbitals, while downwards, polarization favors Ti t(2g) (yz) symmetry. It is predicted that the abrupt (La, Sr)vertical bar TiO2 interface is magnetoelectrically active, leading to a A-type antiferromagnetic coupling of the first TiO2 interface layer with the underlying manganite layer through a superexchange mechanism.

Laser sparks that were built with high-peak power passively Q-switched Nd:YAG/Cr4+:YAG lasers have been used to operate a Renault automobile engine. The design of such a laser spark igniter is discussed. The Nd:YAG/Cr4+:YAG laser delivered pulses with energy of 4 mJ and 0.8-ns duration, corresponding to pulse peak power of 5 MW. The coefficients of variability of maximum pressure (COVPmax) and of indicated mean effective pressure (COVIMEP) and specific emissions like hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx) and carbon dioxide (CO2) were measured at various engine speeds and high loads. Improved engine stability in terms of COVPmax and COVPmax and decreased emissions of CO and HC were obtained for the engine that was run by laser sparks in comparison with classical ignition by electrical spark plugs. (C)2015 Optical Society of America

Thin graphite foils bombarded with an intense high-energy (8.6 MeV/u) gold beam reaching fluences up to 1 x 10(15) ions/cm(2) lead to swelling and electrical resistivity changes. As shown earlier, these effects are diminished with increasing irradiation temperature. The work reported here extends the investigation of beam induced changes of these samples by structural analysis using synchrotron X-ray diffraction and transmission electron microscope. A nearly complete recovery from swelling at irradiation temperatures above about 1500 degrees C is identified. (C) 2015 Elsevier B.V. All rights reserved.

Superconducting bulks of MgB2 were obtained by the Spark Plasma Sintering (SPS) technique. Different heating rates of 20, 100, 235, 355, and 475 degrees C/min were used. Samples have high density, above 95%. The onset critical temperature T-c, is about 38.8 K. There is an optimum heating rate of similar to 100 degrees C/min to maximize the critical current density J(c0), the irreversibility field H-irr, the product (J(c0) x mu H-0(irr)), and to partially avoid formation of undesirable flux jumps at low temperatures. Significant microstructure differences were revealed for samples processed with low and high heating rates in respect to grain boundaries. (C) 2015 Elsevier B.V. All rights reserved.

The occurrence of a second magnetization peak (SMP) on the dc magnetization curves of superconducting single crystals with random quenched disorder in increasing external magnetic field H is quite common. Many models for this intriguing phenomenon have been proposed so far, but its origin is still under strong debate. Optimally doped and overdoped La2-xSrxCuO4 single crystals (x >= 0.15) exhibit an SMP over a large temperature interval, up to very close to the critical temperature. By decreasing doping, it was found that with H oriented along the c axis the SMP completely disappears in the doping domain of well developed static charge and spin stripes (x similar to 1/8), reappearing for x <= 0.10. This behaviour follows the instability of the Bragg vortex glass generated by the static stripe order (as revealed by small-angle neutron scattering experiments), which is confirmed by our magnetization relaxation measurements. If H is along the (a, b) planes, the SMP is observed for all investigated specimens. The presented analysis supports the scenario in which the SMP is generated by the pinning-induced disordering of the low-field Bragg vortex glass in the dynamic conditions of dc magnetic measurements. (C) 2015 Elsevier B.V. All rights reserved.

Thermo-ionic Vacuum Arc evaporation method was selected for the synthesis of Fe/Cu/Ni/Cu multilayer structures on Si (1 0 0) substrates. The aim of the study was the preparation and characterization of structures featuring a giant magnetoresistance effect. This was accomplished by inducing the formation of nanosized ferromagnetic crystallites in multilayer nonmagnetic solutions via atomic inter-diffusion processes by the tuning of deposition parameters. Layer-by-layer and inter-diffused type structures were prepared and comparatively analyzed by scanning electron microscopy, X-ray microanalysis, atomic force microscopy, X-ray diffraction and high-resolution transmission electron microscopy coupled with selected area electron diffraction. We presented the influence of the microstructure on electric and magnetic properties of the submicron-sized multilayers. The dependence of the electric resistance and the magnetoresistance on the composition, structure, morphology and roughness of the layers was established. We obtained an electric resistance value of 1.22 Omega for the layer-by-layer type structure, and 0.46 Omega for the inter-diffusion designed structure. Using the atomic inter-diffusion we succeeded in achieving an improvement of the magnetoresistive effect, from 0.1% to 2.3%. (C) 2015 Elsevier B.V. All rights reserved.

Pyridoxal isonicotinoyl hydrazone (HL) and its copper(II) complexes: [CuLCI(H2O)(2)] (I), [CuL(OAc)](H2O) (2), [CuL(OAcac)] (3), [CuL(NO3)](H2O) (4), [CuL2](H2O) (5) were synthesized and characterized. The ligand has been obtained by condensation of 3-hydroxy-5-(hydroxymethyl)-2-methylpyridine-4-carbaldehyde (pyridoxal) hydrochloride with isonicotinoyl hydrazide. The characterization of the formed compounds was done by H-1 NMR, C-13 NMR, UV-Vis, IR and EPR spectroscopy as well by thermal studies and elemental analysis. The crystal structure of HL has been determined by single crystal X-ray diffraction studies. The microbiological effect of the ligand and all five complexes against both Gram-positive and Gram-negative strains, Staphylococcus aureus ATTC 6538, Bacillus cereus ATCC 14579, Escherichia call W3110 and Pseudomonas aeruginosa ATCC 9027 was tested. (C) 2015 Elsevier Ltd. All rights reserved.