Enhancement of critical current density and flux pinning force of MgB2 by Bi2212 addition

As far as current interest is concerned, the pinning centers of non-ideal type II superconductors are mainly structural defects that apply attractive potential wells to the motion of magnetic flux lines, including nonsuperconducting second phase particles, grain boundaries, etc. In this paper, high-temperature superconductor Bi2212 particles are introduced into MgB2 to explores the behavior of superconducting pinning centers played by superconducting particles that apply repulsive potential barriers to the motion of magnetic flux lines. By mixing ground Bi2212 single crystal with Mg and B powders, (MgB2)1-x(Bi2212)x (x = 0, 3, 5, 7, and 10 wt%) composites were prepared and characterized with XRD, SEM, TEM, and physical property measurements. The irreversible magnetic field Hirr, critical current density Jc, and flux pinning force Fp were enhanced at x = 3 wt%. The best infield-Jc@( 4.2 K, 6 T) reaches 8.1 x 103 A/cm2, which improved the performance by 55.8 % compared to 5.2 x 103 A/cm2 of pure MgB2 sample; and the Jc@(20 K,2 T) reaches 8.0 x 104 A/cm2, which is 1.60 times of the 5.0 x 104 A/cm2 for the pure MgB2 sample under the same conditions. Although the addition of Bi2212 enhances the pinning strength of MgB2, it has no qualitative effect on the flux pinning characteristics, i.e., the flux pinning behavior is still dominated by grain boundary pinning mechanism. It is argued that in this study, Bi2212 particles are likely to exist in the form of nanoparticles in the MgB2 matrix, which contribute to the collective pinning as weak pinning centers.