CRITICAL-CURRENT ENHANCEMENT BY DOPING ME LT-TEXTURED YBCO WITH BASNO3

We have performed critical current density measurements (DC current) o n melt textured YBaCuO doped with BaSnO3 which exhibits transport valu es at 77 K as high as 7.1 x 10(4) A cm-2 in zero field and 1.1 x 10(4) A cm-2 at 20 T. A systematic study of this ceramic has been carried o ut using SEM and HREM observations in correlation with J(c) measuremen ts. A textured microstructure is observed containing numerous green ph ase inclusions (size less-than-or-equal-to 10 mum) as well as a few nu mbers of BaSnO3 inclusions (size < 1 mum). It has been found that tran sport J(c) data are distributed over a wide range (2.5 x 10(3)-7.1 x 1 0(4) A cm-2). Nevertheless, magnetic J(c) measurements suggest that cr acks of the order of several microns may appear in some regions of the material leading to a dramatic decrease of transport J(c) for the cor responding sample. On the other hand, HREM observations demonstrate th at extended defects cannot be considered as the major factor for vorte x pinning in textured 123 material. The presence or the absence of inh omogeneity at the nanoscale does not seem to influence the critical cu rrent density. Finally, it has been determined that pinning can be asc ribed to lamellar microstructure rather than to BaSnO3 inclusions.