Comparative studies of MgB/sub 2//Mg nano-composites and press-sintered MgB/sub 2/ pellets

We present our studies of superconducting and microstructural properties of bulk MgB/sub 2//Mg nano-composites and press-sintered MgB/sub 2/. TEM investigation revealed that the composites are very dense, consisting of nano-sized MgB/sub 2/ grains connected by the well-defined clean grain boundaries (GB). Both amorphous and structural intact GB's were observed in the press-sintered samples. Magnetization and transport measurements showed that the composite carried over 1 MA/cm/sup 2/ critical current density (J/sub c/) at 5 K and self-field, while the pressed sintered MgB/sub 2/ has J/sub c/ /spl sim/ 0.25 MA/cm/sup 2/ at 5 K and self-field. The origin of substantially higher J/sub c/ found in the composites is mostly due to their nano-sized grains and clean grain boundaries.