Bulk samples were prepared which contained 0, 3, 5 or 10wt%Bi2Sr2CaCu2O8 (Bi-2212) particles, added by using a simple solid-state reaction route, in order to investigate the effect of inclusions of a material with higher TC than the superconducting matrix. The density, diamagnetic signal and critical current density of the samples changed significantly with doping level. It was found that JC was significantly enhanced by the Bi-2212 additions. Microstructural analysis indicated that a small amount of Bi-2212 was decomposed into Cu2O and other impurity phases, while a significant amount of unreacted Bi-2212 particles remained in the MgB2 matrix. These acted as effective pinning centers for vortices. The enhanced pinning force was mainly attributable to these highly dispersed inclusions, inserted into the MgB2 grains. In spite of the effectiveness of the high-TC inclusions in increasing the superconducting critical currents in the experiment, the results seemed to demonstrate the superiority of attractive centers over repulsive ones. A pinning mechanism was proposed in order to account for the contribution of this type of pinning center in MgB2 superconductors

Magnetic Properties and Critical Current Density of Bulk MgB2 Polycrystalline with Bi-2212 Addition. T.M.Shen, G.Li, X.T.Zhu, C.H.Cheng, Y.Zhao: Superconductor Science and Technology, 2005, 18, L49-52