Filling of electronic density of states in Y-123 superconducting ceramics by nano Nd substitution on Ba site in crystal structure

摘要

This comprehensive examination focuses on the effect of the Nd substitution on the phase formation, mechanical, microstructural and superconducting properties of YBa2Cu3O7-x ceramics with the aid of standard experimental measurement tecniques as regards X-ray diffraction (XRD), dc resistivity (rho-T), Vickers's microhardness (H-v) and scanning electron microscopy (SEM) measurements. For the full characterization of the pure and Nd substituted Y-123 samples, the onset-offset critical transition temperature, variation of transition temperature, crystal structure, grain size, phase purity and lattice parameters are determined and discussed clearly. The results demonstrate that the crucial characteristics given above improve with the increase in the Nd concentration level at the Ba-site in the superconducting core up until a critical value of x = 0.250 after which the characteristics tend to retrograde rapidly due to the transition of optimally doped state to the underdoped state position in the Y-123 superconducting lattice. This is in association with both the hole localization problem of the electronic states in the vicinity of the Fermi level and the presence of more disordered metallic state. The long and short of it is that the excess (0.250 < x) replacement of Ba inclusions for Nd impurities in the system leads to degradation of the major (Y-123) phase or increment of the minor phase (Y-211) in their intrinsic crystal structures with the phase transition from orthorhombic to pseudotetragonal in the crystal structure, being one of the most striking points deduced from this work. At the same time, the mechanical performance shows the similar trend (firstly increase then decrease) with the increase of the Nd inclusions inserted in the Y-123 superconducting matrix. The Vickers microhardness measurement evidences also declare that the plastic deformation is superior to the elastic deformation (no elastic recovery) in the samples presenting RISE behavior. (C) 2015 Elsevier B.V. All rights reserved.