A practical processing method for the fabrication of high performance, single grain (LRE)-Ba–Cu–O superconductors

We report a practical processing method for the fabrication in air of large, single grain LRE-Ba–Cu–O [(LRE)BCO, where LRE = light rare earth ] superconductors in a simple box-type furnace that exhibit high T c and J c . The technique is potentially economical, offers a significant degree of freedom in terms of both processing parameters and reproducibility in the growth of oriented single grains and yields bulk samples with significantly improved superconducting and field-trapping properties. The process is based initially on the development of a new type of generic seed crystal that can promote effectively the epitaxial nucleation of any (RE)-Ba–Cu–O system, and secondly on the suppression of the formation of (LRE)/Ba solid solution in a controlled manner within large (LRE)BCO grains processed in air. The characteristics of the generic seed are discussed in detail. In addition, the degree of homogeneity of large grain Nd–Ba–Cu–O, Sm–Ba–Cu–O and Gd–Ba–Cu–O superconductors fabricated in air by this novel processing technique has been investigated from the spatial distribution of the superconducting transition temperature and the critical current density along both the a and c growth sectors of each single grain. As a result, the optimum processing conditions for the fabrication of single grains with improved homogeneity and with high J c have been established. Finally, J c of 10 5 A cm −2 has been measured for large grains of Gd–Ba–Cu–O bulk superconductor at 77 K.