Abstract
We have studied the flux-pinning mechanisms of YBa Cu-2 (3) O (y) (Y-123) and YBa Cu-2 (3) O (y) embedded by Y-deficient Y-123 nanoparticles induced by planetary ball-milling technique. Samples were synthesized in air using a standard solid-state reaction technique by considering a thermal cycle with two stages of sintering at 950 A degrees C separated by intermediate crushing; a traditional crushing (in a mortar) and another energetic (in a planetary crusher). Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning electron microscopy (SEM), microstructure investigation by transmission electron microscopy (TEM), and the global critical current density dependence on temperature (J (ct)(T)) at several applied magnetic fields were carried out. The temperature dependence of J (ct)(T) was analyzed within the collective pinning model. For both samples and at self-magnetic field, the temperature dependence of the critical current density is in agreement with the delta T (c) pinning mechanism which is due to the spatial fluctuation of the Ginsburg-Landau coefficient associated with the transition temperature T (c). Under an applied magnetic field of 100 mT there is evidence of delta epsilon and delta l pinning mechanisms in the unmilled sample; however, the delta epsilon pinning is strongly dominant in the milled one These results agree with TEM observations showing the appearance of defects and contrast deformation due to the nanophases generated by ball milling and embedded inside the superconducting matrix.