1,721,317 research outputs found
Real space and Q space analysis of local disorder induced by Al doping in the SmBa2Cu3O6+d superconductor
No full textThe cation substitutions for copper in RBa2Cu3O6+d (R = Y, Ln; 0 < d < 1) high Tc superconductors are widely studied in order to understand their physical properties [1]. In particular Al seems to be a suitable dopant because: i) it is a non-magnetic ion; ii) it substitutes for copper only on Cu1 (0,0,0) site, far from the superconducting planes; iii) its valence state is fixed, making simple the calculation of the total hole concentration; iiii) it is possible to vary the medium range structure of the superconductor throughout an aluminium-clustering process [2]. However, Aluminium doping introduces local disorder in the structure because of its different valence (+3 instead of +1/+2) and local environment (tetrahedric instead of square planar) in respect to copper. In order to fully understand the effect of Al doping on the physical properties of RBa2Cu3O6+d superconductors the nature of this disorder has to be defined. To do so we have investigated some SmBa2Cu3-xAlxO6+d samples with different Al concentration (x=0, 0.15, 0.33), annealed either in oxidising or in reducing conditions. The long and short range structure of the samples have been determined through the parallel real pace (PDF) and Q space (Rietveld) analysis of XRPD patterns obtained at the ID31 beamline of ESRF facility. References
[1] See, for instance, M.S. Skakle, Mater. Sci. Eng., R23, 1 (1998) and references therein
[2] M. Scavini, M. Daldosso, S. Cappelli, C. Oliva, M. Brunelli, C. Ferrero, A. Lascialfari, Europhys. Lett., 76(3), (2006) 443-44
Electron Magnetic Resonance of f-elements-containing perovskite- and ferrite-like compounds
No full textTriple Ion Formation by Dinitrobenzophenone Radical Anion. Effects on the Internal Hindered Rings Rotation
No full textEPR and XRD as probes for activity and durability of LaMnO3 perovskite-like catalysts
No full textFour different LaMnO3 perovskites were prepared by different procedures, characterised and tested for the catalytic flameless combustion of methane. EPR and XRD have been found useful probes for testing activity and durability of the catalysts, respectively. Broader EPR lines correspond to more active catalysts, while high crystallinity indicates long-lived samples
EPR investigation of superparamagnetism in nanometric-size LaFeO3 +/-delta and La2NiO4 +/-delta perovskites
No full textTwo LaFeO3 +/- delta and La2NiO4 +/- delta catalysts characterized by high thermal stability and phase purity have been prepared. Scanning electron microscopy analysis showed that they consisted of 20-60 nm spheroids, generally clustered in one order of magnitude larger particles. Electron paramagnetic resonance (EPR) spectroscopy showed that both samples possess superparamagnetic properties, connected with ca. 20 nm diameter particles. Furthermore, the EPR patterns were broader in La2NiO4 +/- delta, than in LaFeO3 +/- delta, indicating a greater amount of local disorder in the former. This was attributed to the presence of more oxygen vacancies in the Ni-based than in the Fe-based sample, in agreement with what was elsewhere hypothesized on the basis of catalytic properties of the two samples for the flameless combustion of methane
UNDECAD RESOLUTION OF POLYPROPYLENE STEREOSEQUENCES - QUANTITATIVE-EVALUATION OF C-13 NMR METHYL SPECTRUM
No full textThe quantitative evaluation of a 50.3 MHz 13C NMR methyl spectrum of a particular stereoisomer of polypropylene, called hemiisotactic (hit-PP), was performed by a full lineshape fitting procedure. This sample presents a dramatic selection between stereosequences and a characteristic pattern of signal intensities. The results are compared with a general statistical approach, leading to the conclusions that the structure of hit-PP is almost pure (96%). Also, small deviations from the ideality are accounted for. In this way linewidths and chemical shifts have been established for nine nonads and five undecads of monomer units, calling for a sensitivity to carbon atoms distant up to ten bonds
Cr3+ ESR Linewidth in ZnO-ZnCr2O4-(Pd) Solid Mixtures
No full textThe e.s.r. signal generated by a solid catalyst, based on a ZnO, ZnCr2O4 and Pd mixture, has been studied as a function of the concentration of the components. The linewidth broadening and narrowing of the signal is strongly dependent on both the Zn/Cr ratio and the Pd concentration and is connected with a change in the relative distance between the Cr3+ ions
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