1,721,030 research outputs found
A reverse Monte Carlo study of a zinc-europium phosphate glass
No full textA combination of seven independent experimental functions obtained by X-ray diffraction and EXAFS from synchrotron radiation and neutron diffraction techniques were used as references in a reverse Monte Carlo simulation of a glassy sample of 0.1 Eu(PO3)(3)-0.9 Zn(PO3)(2) composition. The final model shows that the phosphate chains essentially retain the structure they have in pure zinc metaphosphate, while zinc and europium ions are set among the chains, so enveloped that oxygens from the PO4 groups create coordination cages. The zinc ions maintain the same environment they have in pure zinc metaphosphate. The europium sites are more complex, made up by a nearest neighbour shell of non-bridging oxygens, to which also a minor number of bridging oxygens contribute at longer distances
An X-ray absorption spectroscopy study of the NiK edge in NiO-SiO2 nanocomposite materials prepared by the sol-gel method
No full textEXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) techniques have been used to study the structural evolution of nanocomposites constituted of nickel oxide nanoparticles embedded into an amorphous silica matrix during their sol-gel preparation. EXAFS data show that no interaction between the metal oxide nanoparticles and the silica network develops since the spectra of all the samples have a structure very similar to that of crystalline NiO. Quantitative information obtained from the fitting of the data using a full multiple scattering calculation shows that the reduction of the EXAFS oscillations in the nanocomposite samples is mainly related to an increase of disorder of the superficial sites while there was no evidence of a significant reduction of coordination numbers due to the size of the crystallites. XANES results support the conclusion that the structure of the nanocomposites is very similar to that of crystalline NiO
A neutron diffraction study of a sodium nickel phosphate glass
No full textThe structure of a sodium nickel phosphate glass has been studied by neutron scattering with isotopic substitution for nickel. The first shell in the first-difference radial distribution function occurs at 2.05 Å, a value corresponding to sixfold Ni-O coordination. The results also indicate that the shell is distorted with two main distances. From the second-difference signals the Ni-Ni correlations have been obtained; a first peak is centered at 3.3 Å and a stronger peak occurs at 6 Å with a shoulder at 4.8 Å
ZnO-SiO2 nanocomposites obtained by impregnation of mesoporous silica
No full textThe synthesis of ZnO-SiO2 nanocomposites through impregnation of a commercial mesoporous silica with zinc nitrate aqueous or ethanolic solutions is reported. During thermal treatment the samples evolve toward the formation of nanocrystalline ZnO particles (zincite phase) dispersed onto amorphous silica stable up to the temperature of 700 degreesC. The nanoparticle size distribution is affected by the process parameters used in the impregnation. A narrower and more homogeneous distribution is obtained using ethanolic instead of aqueous solutions. At higher temperatures the samples evolve towards the formation of a zinc silicate phase. (C) 2003 Elsevier Science Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Sol-Gel Preparation and Characterization of Metal-Silica and Metal Oxide-Silica Nanocomposites in Material Research Foundation
No full textMagnetism in nanoparticles: Beyond the effect of particle size
No full textA set of investigations on selected samples of nanosized cobalt ferrite are reviewed, aimed at studying the various factors affecting the magnetic properties of nanoparticles. Specifically, the effects of inter-particle interactions, of structural and magnetic order, both in the core and on the surface of the particle, have been examined. All factors render the control of the magnetic properties of nanosystems quite difficult, but, at the same time, they also offer the opportunity of tuning them properly, so that materials for specific applications may be created. © 2009 Wiley-VCH Verlag GmbH & Co
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