Fabrication and characterization of LRE_1+xBa_2-xCu₃O_y (LRE: Nd, Eu, Gd, NEG) superconductors: A low oxygen partial pressure

We studied the effect of oxygen partial pressure reduction to 0.05% during melt processing of NdBa₂Cu₃O_y, EuBa₂Cu₃O_y, GdBa₂Cu₃O_y, and (Nd,Eu,Gd)Ba₂Cu₃O_y on magnetic properties and microstructure. The superconducting transition of all the optimally oxygenated samples was as narrow as in those prepared in pO₂ of 0.1%, the onset temperature of the present samples was slightly higher or at least same as for 0.1% pO₂. Optical and scanning electron microscopy showed that in the GdBa₂Cu₃O_y and EuBa₂Cu₃O_y clusters are formed of sub-micron sized secondary phase particles. In other two compounds the secondary phase was uniformly dispersed. Magnetic properties of the present samples were always better at low fields than those of the samples prepared in 0.1% pO₂. The irreversibility field data were rather controversial, in some samples improved, in others worse.