Control of the Nd422 second phase for the improvement of the critical current density in Nd-Ba-Cu-O superconductors

Effects of size and volume fraction of the Nd₄Ba₂Cu₂O₁₀ (Nd422) second phase on the critical current density (J_c) were studied for the Nd-Ba-Cu-O bulk superconductors fabricated by an oxygen-controlled-melt-growth (OCMG) process. The size of the Nd422 second phase trapped in NdBa₂Cu₃O_y (Nd123) superconducting matrix was controlled using two different precursors of Nd123-Nd422 powders and the melt-quenched powders. Finer Nd422 second phase with an average diameter of 1-2μm was obtained in the sample fabricated from the mixture of Nd123-Nd422 precursors when the initial Nd422 powders of less than 1μm was employed. The J_c was significantly improved especially in low field by refining the Nd422 second phase. While a small amount of Nd422 addition increases the J_c in low field without sacrificing the J_c near the fishtail peak, the peak effect was drastically depressed by increasing the volume fraction.