Strong enhancement of Jc and Birr inbinary in situ MgB2 wires after cold high pressure densification

Abstract

Cold high pressure densification was found to substantially enhance the critical current density of binaryin situ Fe/MgB2 wires. A wire densified at 1.85 GPa exhibited at 20 K and 5 T an increase ofJc by 300% with respect to same wire without the application of pressure. At 4.2 K and 10 T,Jc was found to be increased by 53%. The decrease of the electrical resistancefor densified wires reflects an improved connectivity. The values ofBirr at 4.2 and 20 K were enhanced up to 0.7 T for densified wires.After applying pressures up to 6.5 GPa at 300 K, the relative mass densitydm of theunreacted (B+Mg) mixture inside the filament increased up to 96% of thetheoretical density. This corresponds to a relative mass densitydf in thereacted MgB2 filaments of 73%. A quantitative correlation between filament mass density and criticalcurrent density was established.