2D AND 3D PERCOLATION IN HIGH-TEMPERATURE SUPERCONDUCTORS

A quantitative model is presented for the high critical current densit ies (J(c)) supported by superconducting materials with uniaxial alignm ent, such as c-axis textured Bi-Sr-Ca-Cu-O tapes. Current follows perc olative paths across small-angle grain boundaries. Because j(c) is low for intragranular conduction parallel to the c axis, the 3D flow requ ired for percolation is produced by conduction perpendicular to the c axis in tilted grains. For optimized microstructures, J(c) ranging fro m 3 to 30% of the intragranular value is predicted for percolation acr oss small-angle grain boundaries w;ith misorientations below 10 degree s and 20 degrees, respectively.