Improved flux pinning in PMP YBa₂Cu₃O_y superconductors by submicron Y₂BaCuO₅ addition

YBa₂Cu₃O_y samples with varying Y₂BaCuO₅ (211) second-phase concentrations have been prepared using the submicron-sized 211 precursors by a powder melting process method and their critical current density (J_c), flux pinning and microstructure have been investigated. The microstructural observations show that most 211 particles in the sample are submicron in diameter (as small as 300 nm), which can work as effective pinning centers. J_c in low fields increases monotonously with increasing the 211 concentration. A high irreversibility field above 7 T at 77 K in H∥c is observed in these samples. A very high J_c value of 1.6 × 10⁵ A/cm² at 77 K in self-field has been achieved in the sample with 25% 211 addition. A plateau-region of J_c versus field (as high as 60000 A/cm² at 77 K) is also obtained, which is very promising for applications. In addition, the scaling of pinning force as a function of the reduced field gives a peak position of 0.33 which is an indication of pinning provided by normal conducting 211 particles.