Local texture and percolative paths for long-range conduction in high critical current density TlBa₂Ca₂Cu₃O _8+x deposits

A possible microstructural origin of the high critical current densities which have been obtained in c-axis-aligned, polycrystalline TlBa ₂Ca₂Cu₃O_8+x deposits has been identified. The results of x-ray diffraction determinations of basal plane texture of Tl-1223 deposits prepared by spray pyrolysis are observed to depend on the size of the x-ray beam. Furthermore, most grain boundaries were found from transmission electron microscopy to have small misorientation angles. It is concluded that although overall the basal plane orientations are nearly random, there is a high degree of local texture indicative of colonies of similarly oriented grains. The spread in a-axis orientation within a colony is ∼10°-15°. Intercolony conduction, it is suggested, may be enhanced by a percolative network of small-angle grain boundaries at colony interfaces.