Critical current density enhancement in strongly reactive<i>ex situ</i>MgB₂bulk and tapes prepared by high energy milling

Abstract

The ex situ technique is promising for its ease of preparation, low material shrinkage during annealing and the fact that it is already superconducting without annealing. However the critical current density (Jc) needs to be enhanced. To improve the Jc values of commercial powder high energy milling was used—a method commonly use in industry and easy to apply. It was found that high energy milling is successful in improving Jc in bulk and tapes. The reason for the improvement is reduced crystallite size and the large fraction of fresh grain surfaces. In this paper we also experimentally investigate the problem of decomposition of MgB2 ex situ during heat treatment.