Preparation and Properties of New Superconductor Material MgB2
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.
Paula Maria Vilarinho
D. Marinha, F. J. Oliveira, M. S. Reis, F. M. Costa, M. F. Carrasco, J. P. Araújo, J. B. Sousa, J. M. Vieira, V. S. Amaral, "Preparation and Properties of New Superconductor Material MgB2", Materials Science Forum, Vols. 514-516, pp. 333-337, 2006