Effects of silver addition on critical current densities and mechanical properties in bulk MgB₂

The present study focuses on the effects of Ag addition on the critical current density (J_c) and the mechanical performance of disk-shaped MgB₂ bulk superconductors. MgB₂ samples with varying Ag contents of 0, 2, 4, 6, 8, and 10 wt% were sintered at 775°C for 3h in Ar atmosphere. The J_c values were improved with Ag addition, in that the sample with 4wt% Ag showed the highest J_c value of 295kA cm^-2 at 20K and self-field. The respective J_c values of the same sample were 430, 360, and 238kA cm^-2 in self-field, 0.5T, and 1T at 7K. These values are the highest so far reported in bulk MgB₂ materials. Scanning electron microscopy showed that silver and silver oxide particles are embedded in the voids. As a result, the mechanical performance at room temperature was improved with Ag addition. We also confirmed the presence of nanometer-sized AgMg₃ particles, which may be responsible for high flux pinning and improved mechanical performances. The disk-shaped MgB₂ bulk superconducting super-magnets are potential candidates for industrial applications, especially in the medical field. The flux pinning and the mechanical performance of MgB₂ bulk superconductors are dramatically improved by adding 4wt% Ag. The morphology of the Ag particles and their dispersion in the nanoscale can be visualized by SEM and AFM.