The microstructures and superconducting properties of MgB₂ bulks prepared by a high-energy milling method

We succeeded in the synthesis of high-J_c MgB₂ bulks via high energy ball-milling of elemental Mg and B powder at ambient temperatures. The mixed powder was ball-milled for 1-10 h and the completed reaction was achieved by subsequent annealing. The correlations among synthesis parameters, microstructures and superconducting properties in MgB₂ bulks were investigated. Samples were characterized by X-ray diffraction and scanning electron microscope, and the magnetization properties were examined by a superconducting quantum interfere device magnetometer. The highest J_c, approximately 2.3 × 10⁵ A/cm² (15 K, 3 T), was obtained for samples milled for 5 h and sintered at 750 °C for 1 h. It is even comparable with SiC-doped MgB₂ bulks made by Dou's group, which had exhibited the strongest reported flux pinning and the highest J_c in high field to date.