Flux pinning in melt-processed nanocomposite single-grain superconductors

Insulating RE2BaCuO5 (RE-211) second-phase inclusions embedded within the REBa2Cu3O7-delta (RE-123) superconducting phase matrix are known to contribute significantly to flux pinning in melt-processed superconductors. The critical current density in these materials has been observed to increase significantly in the presence of low external magnetic fields, in particular due to the presence of the RE-211 phase. J(c) at higher applied magnetic field, however, is unaffected by these inclusions. Recently we have introduced successfully nanoscale (RE)(2)Ba4CuMOy (RE-2411, where M = W, Nb, Ag and Bi) phase inclusions into the RE-123 phase matrix using a top-seeded melt growth (TSMG) technique. Here we report the flux pinning behaviour of various REBa2Cu3O7-delta/(RE)(2)Ba4CuMOy nanocomposites and compare their properties with those of REBa2Cu3O7-delta/RE2BaCuO5 single-grain composites. A direct correlation between increased Jc and increased concentration of nanoscale inclusions is observed. Finally, the presence of RE-2411 nanoscale inclusions is observed generally to improve both Jc and the irreversibility field of bulk RE-Ba-Cu-O superconductors processed by TSMG.