Critical current densities in Ag-added bulk MgB2

•Bulk MgB2 samples with Ag contents of 0–10 wt% were sintered at 775 °C for 3 h.•Magnetization measurements showed a sharp superconducting transition with Tc (onset) around 38.5–38.7 K.•Atomic force microscopy indicated that Ag-based MgB2 particles are of nanometer size.•The sample with 4 wt% Ag addition exhibited the highest Jc of 400 kA/cm2 at 10 K and self field.

In previous studies, we found that bulk MgB2 contained numerous voids in various shapes and sizes. With the aim of improving the critical current density as well as the mechanical performance of the disk-shaped MgB2 bulk superconductors, we added Ag and optimized the processing conditions. The samples with varied Ag content from 0, 2, 4, 6, to 10 wt% were synthesized in pure Ar atmosphere. Microstructural observation by scanning electron microscopy confirmed that metallic Ag particles are embedded in the void regions. Furthermore, atomic force microscopy indicated that silver-based MgB2 particles are of nanometer size. As a result, the critical current density (Jc) values were improved with Ag addition as compared to pure MgB2 bulk. The sample with 4 wt% Ag addition exhibited the highest Jc of 293 kA/cm2 at 20 K and self field. The respective Jc values at 10 K were 400 kA/cm2, 300 kA/cm2, and 100 kA/cm2 in self field, 1 T and 2 T. These values are the highest record values so far reported in bulk MgB2 materials.