FLUX-PINNING IN MELT-PROCESSED RE-BA-CU-O

RE-Ba-Cu-O (RE: rare earth element selected from Nd, Sm, Eu, Gd) super conductors exhibit high T-c and J(c) values when they are melt process ed in a reduced oxygen atmosphere (oxygen-controlled-melt-growth: OCMG process). Large J(c) values in these systems can be attributed to fin ely dispersed RE rich 123 clusters, which can act as field-induced pin ning centers, and thus leading to the second peak effect in M-H loops. In this paper, we first propose the mechanism how RE rich clusters ar e formed during melt processing. Second we show that flux pinning depe nds on oxygen annealing conditions, because the optimum oxygenation co nditions are different depending on the range of Nd-Ba substition. We also report that the addition of Nd422 is effective in raising J(C), a lthough the mechanism is rather complicated owing to the fact that Nd4 22 also has a RE-Ba solid solution toward Ba rich direction.