National Institute Of Materials Physics - Romania

The formation and crystallization of disordered nanosized ZnO resulting from the thermal decomposition of nanocrystalline hydrozincite [Zn-5(CO3)(2)(OH)(6)] has been Observed and investigated during pulse annealing experiments Up to 625 degrees C in air or vacuum by electron paramagnetic resonance of trace amounts of substitutional Mn2+ impurity ions, in correlation with X-ray diffraction and transmission electron microscopy measurements. The mesoporous structure of the disordered ZnO, which initially forms in air and vacuum at 225 and 175 degrees C, respectively, further transforms into nanocrystalline ZnO of increasing particle size and improved lattice quality at higher annealing temperatures. The crystallization process, which does not affect the concentration of the substitutional impurity ions, as well as the simultaneous presence of both disordered and crystalline phases, should be considered in further applications of the resulting nanosized ZnO.

This study reports a two-steps route for obtaining magnetic nanoparticles-polysaccharide hybrid materials consisting of Fe3O4, NiFe2O4 and CuFe2O4 nanoparticles synthesis by coprecipitation method in the presence of a soft template followed by coating of ferrite nanoparticles of 8-10-nm size range with polysaccharide type polymers-sodium alginate or chitosan. Magnetic oxide nanoparticles and the corresponding hybrid materials were characterized by X-ray diffraction (XRD), Mossbauer spectroscopy, atomic absorption spectroscopy (AAS), FTIR spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and specific surface area measurements. The vibrating sample magnetometry confirms the superparamagnetic properties of the synthesized ferrites and hybrids. Using this route, the percent of magnetic nanoparticles retained in chitosan-based hybrid materials is nearly double in comparison with that of sodium alginate-based materials. The biological activity tests on Escherichia coli ATCC 25922, Pseudomonas aeroginosa ATCC 27853, Staphylococcus aureus ATCC 25923 and Candida scotti microorganisms show the non-toxic properties of prepared hybrid materials.

Due to its low resistivity and excellent thermal stability, IrO2 has attracted attention as an alternative for electrode material in ferroelectric integrated circuit applications. Oriented growth of IrO2 electrode film was investigated with the goal to control the texture of the PZT thin film. IrO2 films were prepared by DC reactive sputtering. PZT film was prepared by RF magnetron sputtering single target deposition method. The whole layer stack was grown onto amorphous thermal oxide of a silicon wafer. The results indicate that IrO2 thin film was preferentially (200) oriented when a TiO2 seeding layer was used. The orientation relationships along the whole PZT(111)/IrO2(200)/TiO2(200)/Ti structure was discussed.

BaTi0.87Sn0.13O3 (BTS13) nanopowder was prepared by low-temperature aqueous synthesis (LTAS) method. The evolution of the structure and microstructure of the precursor precipitate, heated at temperatures up to 1000 degrees C was studied by TGA, FT-IR, SEM and XRD techniques. The dried precipitate showed a microstructure consisting of nano-sized grains (similar to 40 nm) with great tendency to agglomeration. BaTi0.87Sn0.13O3 single phase was obtained at 800 degrees C. The ceramics prepared from as-obtained BTS13 powders (60-70 nm) show good dielectric and ferroelectric characteristics. The dielectric constant was about 4800 and the dielectric loss (tan delta) was 0.229 at 1 kHz and at the Curie temperature (31 degrees C). The remanent polarization (P-r) and the coercive field (E-C) of Ba0.97Ho0.03TiO3 ceramics, at 1 kHz, were P-r = 13 mu C/cm(2) and E-C = 0.89 kV/cm. The ferroelectric parameters E-C and P-r decrease with increasing frequency in the domain 100 Hz to 10 kHz. (C) 2011 Elsevier B.V. All rights reserved.

The thermoluminescence (TL) response to gamma-ray irradiation of tooth enamel is reported. The tooth enamel was separated from dentine by using mechanical and physico-chemical procedures followed by grinding (grain size 100 urn) and etching. Then was attributed to the recombination of CO(2)(-) radicals incorporated into or attached to the surface of hydroxyapatite crystals. The growth of the 380 degrees C peak with absorbed dose was examined with irradiated tooth enamel samples and reconstructed doses evaluated for tooth enamel samples from four human subjects. (C) 2011 Elsevier Ltd. All rights reserved.

There was discovered a material with strong photoconduction effect. Langmuir-Blodgett film with barium stearate, and selenium carbazole has been prepared and tested for the change of conductivity (decrease) under the influence of UV-radiation. Change of resistance in a time scale of 0-400 seconds was evidenced. The UV radiation determines an increase of the electrical resistence and after switching off the illumination a slow decrease of the resistance occurs.

A mesoporous structure of self-assembled nanocrystals of cubic ZnS doped with Mn2+ ions with a homogeneous distribution of pores of similar size was synthesized at room temperature by a surfactant-assisted liquid-liquid reaction. The component nanocrystals exhibit a high crystallinity and a tight size distribution centered at 2 nm, as well as the narrowest Electron Paramagnetic Resonance (EPA) spectra linewidth and the best resolution reported so-far, effects attributed to self-assembling. The observed EPA spectra consist of lines from the substitutional Mn2+(I) and surface Mn2+(II) and Mn2+(III) centers. Here we show that, in contrast with previous reports, our EPA spectra are highly sensitive to structural changes during pulse annealing in vacuum up to 500 degrees C. The changes are related to the transformation of the surface Mn2+ centers in new Mn2+ centers, attributed to an oxidation process in which the thermal decomposition of the Tween 20 additive, also observed by EPA, seems to be involved. We have also been able to observe, for the first time by EPR spectroscopy, the formation of the ZnO phase and the nanocrystals size increase, which occur during annealing up to 500 degrees C, structural changes confirmed by XRD and TEM observations on the samples previously investigated by EPR.

The first field for magnetic flux penetration H in Bi2Sr2CaCu2O8+delta (Bi-2212) single crystals near the critical temperature T-c was investigated from the local magnetic hysteresis loops registered for different magnetic field H sweeping rates by using a scanning Hall probe microscope (SHPM) with similar to 1 mu m effective spatial resolution. Evidences for a significant role of the surface barrier were obtained: the asymmetric shape of the magnetization loops and an anomalous change in the slope of H-p(T) close to T-c. (C) 2011 Elsevier B.V. All rights reserved.

Well-dispersed, uniform monometallic Pt and bimetallic Pt-Cu, and Pt-Ag nanoparticles protected with PVP have been synthesized by a modified-protocol alkaline polyol method. The nanoparticles were characterized by various methods (TEM, XPS, and XRD) to elucidate the relationship between morphology and preparation variables. The average of monodispersed nanoparticles ranged between 4.1 and 4.9 nm. Core-shell structure was obtained in the case of bimetallic nanoparticles. The core of bimetallic nanoparticles was found to be rich in platinum, whereas the shell contained mostly copper or silver. The final structure of bimetallic nanoparticles was found to be determined by the morphology particles resulted in the first reduction step. Explanations are advanced on the light of experimental results.