The connective nature of YBa 2Cu 3O 7 bulk samples studied by inductive critical current measurements

Abstract

The critical current density j c of polycrystalline YBa 2Cu 3O 7 is severely affected by two limiting facts: the anisotropy of the upper critical field, which drives unfavourably oriented grains normal, and the weak intergrain coupling. We have studied the latter effect by an inductive determination of j c which allows to distinguish between the intragrain and the intergrain critical current in the same measurement. The intragrain current density is about 5.10 5 A/cm 2 at 77 K in zero magnetic field, most probably determined by twin boundary pinning, whereas typical values of 5.10 2 are found for the intergrain critical current density. The dependence of the intergrain j c on field and temperature indicates that a Josephson coupling mechanism between the grains is the j c limiting process.