Influence of microstructures and crystalline defects on the superconductivity of MgB[sub 2].

This work studies the influence of microstructures and crystalline defects on the superconductivity of MgB[sub 2], with the objective to improve its flux pinning. A MgB[sub 2] sample pellet that was hot isostatic pressed (HIPed) was found to have significantly increased critical current density (J[sub c]) at higher fields than its un-HIPed counterpart. The HIPed sample had a J[sub c] of 10 000 A/cm² in 50 000 Oe (5 T) at 5 K. This was 20 times higher than that of the un-HIPed sample, and the same as the best J[sub c] reported by other research groups. Microstructures observed in scanning and transmission electron microscopy indicate that the HIP process eliminated porosity present in the MgB[sub 2] pellet resulting in an improved intergrain connectivity. Such improvement in intergrain connectivity was believed to prevent the steep J[sub c] drop with magnetic field H that occurred in the un-HIPed MgB[sub 2] pellet at H >45 000 Oe(4.5 T) and T = 5 K. The HIP process was also found to disperse the MgO that existed at the grain boundaries of the un-HIPed MgB[sub 2] pellet and to generate more dislocations in the pellets. These dispersed MgO particles and dislocations improved flux pinning also at H < 45 000 Oe. The HIPing process was also found to lower the resistivity at room temperature. [ABSTRACT FROM AUTHOR]