An oxygen-controlled melt growth (OCMG) process has been employed for NdBa2Cu3Oy (Nd123) and SmBa2Cu3Oy (Sm123) superconductors for a comparative study. Both Nd123 and Sm123 samples melt-grown in reduced oxygen atmospheres exhibited an enhanced superconducting transition temperature (TC) with a sharp transition and large critical current density (JC) in a high field region at 77 K and for the applied field parallel to the c-axis of samples (H//c). For Nd123, a preferential formation of high Tcphase in a low oxygen partial pressure (PO2) could be qualitatively described considering the thermodynamic stability boundaries of the Nd1+xBa2-xCu3Oy solid solutions on the LOG[PO2] vs 1/T (K-1) phase diagram. A long-term oxygen annealing study for an OCMG-processed Nd123 sample revealed that the annealing temperature should be as low as 300°C.
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