Melt processing for obtaining NdBa₂Cu₃O_y superconductors with high T_c and large J_c

A reduced oxygen atmosphere during melt processing turned out to be critical for the fabrication of NdBa₂Cu₃O_y (Nd123) superconductors possessing high superconducting transition temperature (T_c) with a sharp transition and large critical current density (J_c) at 77 K. In a dc magnetization measurement, Nd123 superconductors melt processed in flowing a mixture gas of 1% O₂ in Ar exhibited the T_c of about 95 K and the transition width of 1.5 K with the applied field of 10 Oe. A four-probe measurement showed the zero resistive transition T_c (R=0) of about 95 K. An anomalous peak effect in the magnetization hysteresis (M-H) loops was commonly observed and lead to large magnetic J_c of 2×10⁴ A/cm² at 77 K and 2 T for the applied field H parallel to the c axis of a sample (H∥c). This achievement is attributable to a preferential formation of high T _c phase (x<0.1) among the Nd_1+xBa_2-xCu ₃O_y solid solutions in a reduced oxygen atmosphere.