The applicability of superconducting tapes is evaluated employing the definition of an irreversibility strain irr , attained at a critical current density J c of 98% of its initial value. Before reaching this limit, the J c decreases slowly. In order to determine the microstructural changes responsible for this behaviour, we investigated the mechanical response of 19-filament BSSCCO-Ag tapes with different ceramic microstructures, when bent without exceeding irr . After chemically removing a rectangular-shaped area of the silver sheath to expose the ceramic filaments, the samples were subjected to three-point bending inside an SEM chamber. Thus, we were able to follow the microstructural changes produced by the formation and propagation of cracks at the same time that we recorded on a PC the force versus deflection curves. We identified three different regions representing the response of the tapes to increasing bending. After the elastic region, the pre-existing microstructural faults determined the plastic behaviour. At higher deflections, we measured several stress drops coincident with the observation of micro-cracks that grew slowly across the filaments. Twin samples were employed to control the critical current density decay as a function of the bending deflection introduced at ambient temperature. We investigated the correlation between the bending induced defects and the critical current degradation.

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The discovery of superconductivity at 39 K in MgB 2 has been catching the attention of scientists due to the possibility of applying the material in magnets and electronic devices operating with cryocoolers (temperatures around 20 K). In the present work, a methodology to optimize the critical current densities of this material is described. MgB 2 bulk samples were prepared and analyzed with the addition of other diborides with the same C32 hexagonal structure as MgB 2 (TaB 2 , ZrB 2 , VB 2 , and AlB 2 ) and with simultaneous addition of SiC. Microstructural characterization, performed using SEM+EDS and XRD, was extremely important to determine the distribution and compositional characterization of the superconducting phase. Magnetic superconducting characterization using SQUID was performed to determine the best material addition. As a result we could analyze the behavior of each addition on the current transport capacity, including an analysis of the magnetic flux pinning mechanisms.Index Terms-Addition of diborides and SiC, crystallography, MgB 2 superconductors, microstructure, superconducting properties.