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Joseph B.,Elettra - Sincrotrone Trieste | Iadecola A.,European Synchrotron Radiation Facility | Bernasconi A.,European Synchrotron Radiation Facility | Rispoli P.,Istituto Tecnologie Avanzate | And 4 more authors.
Journal of Physics and Chemistry of Solids | Year: 2015

A comparative local structure study of pnictide superconductors Ca0.82La0.18FeAs2 (112-type, T c~ 40K) and Ba0.64K0.36Fe2As2 (122-type, T c~ 37K), using room temperature x-ray total scattering measurements is reported. The Fe-As superconducting active layer is found to be globally similar in both the systems consisting of edge-sharing FeAs4/4 tetrahedra as in all the iron-pnictide superconductors discovered so far. Although optimally superconducting, the active layer in these compounds is found to sustain a large local inhomogeneity. These results thus imply that a nanoscopic manipulation of the Fe-As active layer, rather than its isotropic structural tuning, is the key parameter to control the superconducting properties of the iron-based systems. © 2015 Elsevier Ltd.


Joseph B.,Elettra - Sincrotrone Trieste | Iadecola A.,European Synchrotron Radiation Facility | Bernasconi A.,European Synchrotron Radiation Facility | Rispoli P.,Istituto Tecnologie Avanzate | And 4 more authors.
Journal of Physics and Chemistry of Solids | Year: 2015

A comparative local structure study of pnictide superconductors Ca0.82La0.18FeAs2 (112-type, Tc∼ 40 K) and Ba0.64K0.36Fe2As2 (122-type, Tc∼ 37 K), using room temperature x-ray total scattering measurements is reported. The Fe-As superconducting active layer is found to be globally similar in both the systems consisting of edge-sharing FeAs4/4 tetrahedra as in all the iron-pnictide superconductors discovered so far. Although optimally superconducting, the active layer in these compounds is found to sustain a large local inhomogeneity. These results thus imply that a nanoscopic manipulation of the Fe-As active layer, rather than its isotropic structural tuning, is the key parameter to control the superconducting properties of the iron-based systems. © 2015 Elsevier Ltd. All rights reserved.


Margarone D.,ASCR Institute of Physics Prague | Krasa J.,ASCR Institute of Physics Prague | Prokupek J.,ASCR Institute of Physics Prague | Velyhan A.,ASCR Institute of Physics Prague | And 19 more authors.
Review of Scientific Instruments | Year: 2012

An overview of the last experimental campaigns on laser-driven ion acceleration performed at the PALS facility in Prague is given. Both the 2 TW, sub-nanosecond iodine laser system and the 20 TW, femtosecond Ti:sapphire laser, recently installed at PALS, are used along our experiments performed in the intensity range 1016-1019 Wcm2. The main goal of our studies was to generate high energy, high current ion streams at relatively low laser intensities. The discussed experimental investigations show promising results in terms of maximum ion energy and current density, which make the laser-accelerated ion beams a candidate for new-generation ion sources to be employed in medicine, nuclear physics, matter physics, and industry. © 2012 American Institute of Physics.


Joseph B.,University of Rome La Sapienza | Schiavo B.,Istituto Tecnologie Avanzate | Schiavo B.,University of Palermo | D'Al Staiti G.,Istituto Tecnologie Avanzate | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2011

Nano-structured LaNi 5 hydrogen storage materials prepared by ball-milling is analysed using differential scanning calorimetry (DSC) and x-ray photoelectron spectroscopy (XPS). DSC results indicate a partial elimination of defects at 500 °C in a more efficient way for the short-time ball-milled powders compared to the long-time ball-milled ones. XPS results show almost no change in the core-level electronic structure for La and Ni of LaNi 5 in the bulk and the nano-structured forms, but gives an indication that the self-restoring mechanism of the active surface observed in the bulk sample (Siegmann et al. Phys. Rev. Lett. 40, 972) may not be occurring in the nano-powders. Results from the X-ray diffraction and the local structural studies together with the above observations suggest that the reduced unit-cell volume and the enhanced atomic disorder in the nano-structured LaNi 5 cause a larger energy barrier for the hydrogen sorption reactions of the long-time ball-milled samples. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.

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