DEPENDENCE OF CRITICAL-CURRENT DENSITY AND IRREVERSIBILITY FIELD ON THE OXYGEN DISORDERING FOR SINGLE-DOMAIN MELT-TEXTURED Y-123

Large Y-123 single domain textured sample was produced by slowly cooli ng Y-123 + 15% Y-211 precursor seeded with Sm-123 through the peritect ic point. The sample was annealed in flowing O-2 at 380 degrees C for 72 h. An O-2 distribution gradient in the range of 6.64-6.84 was deter mined in the volume of the sample by measuring 'c' parameter of unit c ell for the small cleaved sections. The J(c) of those sections was der ived from hysteresis loops and T-c from a.c. susceptibility. T-c is pr actically constant in the range = 6.84 > x(0) > 6.71 and drops sharply for smaller x(0). A maximum J(c) of 76,000 A/cm(2) (77 K, self field) and an irreversibility field H-irr = 7.2 T were obtained for x(0) = 6 .77, which is in the range of structural transformation of orthorhombi c I-->orthorhombic II phase of oxygen superlattice, where the clusteri ng in the oxygen superlattice is maximal. This results in a strong flu x pinning, giving large J(c) and H-irr. Any-minute deviation from x(0) = 6.77 lowers J(c) and Hi, substantially. (C) 1998 Elsevier Science B .V.