The present study focuses on the effects of Ag addition on the critical current density (Jc) 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 Jc values were improved with Ag addition, in that the sample with 4wt% Ag showed the highest Jc value of 295kA cm-2 at 20K and self-field. The respective Jc 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.
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