Refinement of secondary phase particles for high critical current densities in (Nd,Eu,Gd)–Ba–Cu–O superconductors

Abstract

We have prepared (Nd 0.33Eu 0.33Gd 0.33)Ba 2Cu 3O y (`NEG') superconductors by means of melt-processing under a partial oxygen pressure of 0.1%. In these samples, we achieved a large critical current density, J c, of 6.8×10 4 A/cm 2 at T=77 K and in an applied magnetic field, H a=2.5 T. Furthermore, the irreversibility field, H irr, exceeds 7 T at 77 K for fields applied parallel to the c-axis of the sample. As additional pinning sites, we introduced up to 40 mol% (Nd,Eu,Gd) 2BaCuO 5 (NEG-211) particles plus Pt in analogy to YBa 2Cu 3O y (YBCO) melt-processed superconductors. Microstructural observations clarified that the Pt addition was effective in reducing the size of NEG-211 second-phase particles, which led to a dramatic increase in J c as compared to melt-processed YBa 2Cu 3O y and NdBa 2Cu 3O y (NdBCO). A pronounced secondary peak effect was observed in all magnetization curves obtained at 77 K, however, there is a considerable change in the shape of the magnetization loops as a function of NEG-211 content, which demonstrates the pinning provided by the NEG-211 particles in addition to the δ T c-pinning caused by fluctuation in the transition temperature, T c, like in ordinary NdBa 2Cu 3O y superconductors.