Effects of second phase and platinum additions on the microstructure and the critical current density of OCMG processed (Nd, Eu, Gd)-Ba-Cu-O

We have investigated the effects of second phase (Nd, Eu, Gd)₂BaCuO₅ (NEG211) and platinum addition on the superconducting properties for (Nd, Eu, Gd)Ba₂CUsOy (NEG123) composite prepared by the oxygen-controlled melt-growth (OCMG) process. The addition of NEG211 slightly decreased the critical temperature (T_c) and increased the critical current density (J_c), particularly in a low field region. The secondary peak effect, which is commonly observed in OCMG processed Nd123, was reduced with the NEG211 addition of >10%. Refinement of the NEG211 second phase was achieved by Pt addition, which led to a dramatic increase in both J_c values and the irreversibility field. Low field J_c varied as V_f/d, where V_fis the volume fraction and d is the mean diameter of NEG211, supporting the idea that the 211/123 matrix is responsible for the pinning-like melt-processed Y-Ba-Cu -O. However, in a high field region, due to the presence of additional pinning by field-induced pinning centers, such a relationship is not observed. Our results suggests that fine distribution of the second phase is effective in improving pinning properties in the (Nd, Eu, Gd)-Ba-Cu-O composite.