Melt processing of (rare earth)-Ba-Cu-O bulk superconductors

Several research efforts on improving the performance of melt-processed bulk superconductors are reported. First, we extended our study on the Nd-Eu-Gd (NEG) system by exploring the effect of ball milling the secondary phase powders of the precursor, and observed an increase in the critical current density (Jc) as well as in the trapped field. We also studied the effect of changing the ratio of the rare earth elements of the secondary phase powders of the NEG system. The samples prepared with a larger amount of Gd were found to trap a larger magnetic field without fracturing. On the other hand, the samples with a nominally Nd-rich composition showed a somewhat lower critical temperature. We also studied the effect of doping Zn into DyBCO, and found a favourable influence in terms of Jc and trapped field. Calculations of the magnetic flux density above a field-trapped superconductor indicated that increasing the domain size is very effective to improve the performance of the superconductor even if the larger sample cannot be prepared with the same quality as a smaller one. Therefore, we studied the melt-processing of SmBCO superconductors that are 60 mm in diameter. It was crucially important to release a sufficient amount of oxygen from the melt for the preparation of a homogeneous sample, and it is demonstrated that the magnetic flux usable in applications significantly increased on enlarging the domain size