Enhanced critical current density in undoped MgB2 prepared by in situ/ex situ combination technique

• Enhanced Jc, Birr, and FP have been achieved using in situ/ex situ combination method in MgB2.
• Addition of 25 wt% of ex situ MgB2 is optimum for the best low-field Jc(H) performance.
• The method is simple and easy to scale up for commercial application.

In this paper we report remarkable enhancement of critical current density (Jc) in undoped MgB2 prepared by in situ/ex situ combination method. We optimize the weight percentage of the ex situ MgB2 and find that the addition of 25 wt% of ex situ MgB2 gives the best result. At 20 K, Jc (0 T) and Jc (3 T) reach to 5.2×105 A/cm2 and 3.3×104 A/cm2, respectively. These enhancements are 1.7 times with respect to the in situ preparation. At 5 K, Jc (3 T) and Jc (6 T) are 1.9×105 A/cm2 and 2×104 A/cm2 respectively, which are 2.4 and 4.3 times that of the in situ preparation. Resistivity measurement shows a decrease in connectivity while mass density is increased in the in situ/ex situ combined samples. There is decrease in crystallite sizes which gives rise to the enhancement in pinning forces. The combined effect of connectivity and pinning force enhances Jc (H, T) up to 25 wt% ex situ MgB2 while further additions degrade Jc (H, T).