Papers by Author: Florinda M. Costa

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Authors: V.M. Silva, A.J.S. Fernandes, Florinda M. Costa, J. Sacramento, Rui F. Silva
Authors: M. Boutinguiza, F. Quintero, Manuel Belmonte, A.J.S. Fernandes, Florinda M. Costa, Rui F. Silva, Juan Pou, Mariano Pérez Amor
Authors: D. Marinha, Filipe J. Oliveira, Mário S. Reis, Florinda M. Costa, Maria Fátima Carrasco, João P. Araújo, João Bessa Sousa, Joaquim M. Vieira, Vitor S. Amaral
Abstract: Bulk MgB2 samples were synthesized by hot isostatic pressing under pressures up to 200MPa at 950°C. In these conditions, full densification of samples was obtained (~98% of theoretical density). SEM, EDS and XRD analysis on final dense bodies were used to evaluate samples, and show increasingly better control over the amounts of secondary MgO (down to ~10%) and complete prevention of formation of MgB4 by using simple glass encapsulation techniques and addition of Mg(s) to the capsule. The samples display superconducting properties, including a narrow critical transition in electrical properties (Tc ~36-38K). Magnetic studies were performed, allowing the determination of the superconducting fraction and critical current density Jc of the materials. Contrary to the Tc, the Jc is quite sensitive to the processing and microstructure and values from 0.3 to 0.6x106 A/cm2 are obtained at 10K. The reduction of Jc with the applied magnetic field requires further improvements to reduce weak links.
Authors: Maria Fátima Carrasco, Jorge Monteiro, Vitor S. Amaral, Rui F. Silva, Joaquim M. Vieira, Florinda M. Costa
Abstract: Superconducting fibres of Bi-Sr-Ca-Cu-O system were grown by the conventional Laser Floating Zone (LFZ) process and by the new technique of Electrical Assisted Laser Floating Zone (EALFZ). The presence of an electric field during solidification process significantly changes the fibre microstructure with Bi2Sr2Ca2Cu3O10 nominal composition. The higher cristallinity of the asgrown EALFZ fibres, resulting from the current application during solidification, leads to a transformation rate enhancement during subsequent annealing. A strong correlation between the transport properties and the final microstructure of the annealed fibres is observed. The highest critical current density of the EALFZ fibres is obtained after heat treatment at 845°C while for the LFZ ones similar values are obtained only after annealing at 860°C.
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