The Influence of Synthesis Parameters on Microstructures and   Superconducting Properties of MgB2 Bulks
  We succeeded in the synthesis of high-Jc MgB2 bulks via high energy ball-milling of elemental Mg and B powder at ambient temperatures. Alternatively to longtime mechanical alloying technique, the mixed powder was ball-milled for only 1h and the completed reaction is achieved by subsequent annealing. The correlations among synthesis parameters, microstructures and superconducting properties in MgB2 bulks were investigated. Samples were characterized by XRD and SEM, and the magnetization properties were examined in a SQUID magnetometer. The high- Jc, approximately 1.7*106A/cm2(15K, 0.59T), and improved flux pinning were attribute to a large number of grain boundaries provided by small grain size. 
Y. F. Wu, Y. Feng, G. Yan, J. S. Li, H. P. Tang, S. K. Chen, Y. Zhao,   M. H. Pu, H. L. Xu, C. S. Li, Y. F. Lu