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A reduced oxygen atmosphere during melt processing turned out to be critical for the fabrication of NdBa2Cu3Oy (Nd123) superconductors possessing high superconducting transition temperature (Tc) with a sharp transition and large critical current density (Jc) at 77 K. In a dc magnetization measurement, Nd123 superconductors melt processed in flowing a mixture gas of 1% O2 in Ar exhibited the Tc 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 Tc (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 Jc 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 Tc phase (x

By measuring the magnetization hysteresis, we studied the critical current density, Jc, and irreversibility fields, Hirr, of a c‐axis aligned Hg‐Ba‐Ca‐Cu‐O sample doped with Pb containing the Hg‐1223 phase as the main phase. Anisotropy in ΔM was clearly observed in two different magnetic field directions. Even though the Hg‐1223 phase contains three CuO2 sheets, the Hirr vs [1‐(T/Tc)] curve was located at roughly the same positions as those reported for the Hg‐1201 and Hg‐1212 phases, indicating that the higher Tc phase, i.e., Hg‐1223, is advantageous to the other phases in practical uses.