New understanding of the role of Ag at undeformed Ag/Bi,Pb(2223) interface: texturing and outgrowths

Abstract

The role of Ag at the Ag/Bi,Pb(2223) interface on the texture development was revisited using unusual experimental conditions. The Ag/BiSCCO interface of tapes was reproduced without the heavy deformation process commonly employed in the tape fabrication, in order to eliminate the pre-texturing of the Bi,Pb(2212) phase in the precursor powder. The observed Bi,Pb(2223) texture development was found to be exclusively ascribed to the presence of Ag. Even without mechanical pre-texturing of the Bi,Pb(2212) phase precursor, Ag was found to promote the formation of a textured layer of Bi,Pb(2212) at the early stages of sintering. This textured layer gives rise to the formation of aligned Bi,Pb(2223) grains, thus inducing the alignment of subsequent Bi,Pb(2223) platelets. The new finding is that the alignment reaches deep inside the ceramic core up to 10 µm depth from Ag surface. The influence of the individual Ag grain orientations on the Bi,Pb(2223) outgrowth formation was also investigated. The average length and misorientation angle of the outgrowths are not correlated to the Ag grain orientation. Their density and volume are also found to be independent of the orientation of neighbouring Ag grains. The influence of the Ag thickness on the outgrowth formation was studied using a stepped Ag foil with thickness ranging from 25 µm to 500 µm. The average length and angle of the outgrowths remain constant, regardless of the Ag thickness. However, the linear density and ratio of outgrowths located at the grain boundaries were strongly reduced when the Ag thickness was less than 100 µm.