Engineering of J_c-B characteristics of RE-Ba-Cu-O melt-textured superconductors

A skilful combination of different types of pinning centers with the aim to optimize J_c(B) performance of bulk superconductors in a wide range of magnetic fields is demonstrated on melt-textured (Nd,Eu,Gd)Ba₂Cu₃O_7-δ and NdBa₂Cu₃O_7-δ materials. In this contribution we show (i) the distinct effect of different types of micrometer-size secondary phase particles on J_c(B) dependence at low fields; (ii) possibility to produce materials with either high-current densities at moderate fields or with a flat J_c(B) curve extending to high fields, via appropriate choice of Nd:Eu:Gd ratio in NEG-123 matrix; (iii) extremely high-irreversibility field (≈9 T at 77 K) in NEG-123 samples Eu/Gd > 1 and a small content of NEG-211; (iv) twin structure effect in melt-textured Nd-123 doped by micron-sized Nd-211 particles resulting at low temperatures in a field independent J_c(B) extending to very high fields (at 40 K above 10 T). Vast majority of the data could be interpreted in terms of additive contributions of pinning on point-like and large defects.