Microstructural analysis of high critical current density Ag-clad BiSrCaCuO (2:2:1:2) tapes

Abstract The critical current density ( J c ) values of variously processed Ag-clad Bi 2 Sr 2 Ca 1 Cu 2 O x tapes are related to their microstructures as observed by TEM, SEM, and X-ray pole figure analysis. The coupled microstructure- J c results confirm the general importance of a highly c -axis aligned microstructure for high critical current density. However, TEM experiments revealed a “colony” microstructure in all sample in which groups of several grains with nearly perfect c -axis alignment (colonies) are formed but where the c -axes of adjacent colonies are not parallel. SEM imaging of etched cross-sections showed that important features of this colony misalignment are not accurately reflected by stand alone X-ray pole-figure analysis or TEM imaging. Near-perfect alignment occurs within a few microns of the Ag cladding for all processing methods. However, the processing details control the macroscopic grain alignment within the bulk of the superconductor. In particular, second-phase particles disrupt the alignment of macroscopic colonies. These misalignments may control the transport critical current, yet they are not clearly evidenced by either macroscopic pole-figure analysis or by very local TEM examination.