LOCAL TEXTURE AND PERCOLATIVE PATHS FOR LONG-RANGE CONDUCTION IN HIGHCRITICAL-CURRENT DENSITY TLBA2CA2CU3O8+X DEPOSITS

A possible microstructural origin of the high critical current densiti es which have been obtained in c-axis-aligned, polycrystalline TlBa2Ca 2Cu3O8+x deposits has been identified. The results of x-ray diffractio n determinations of basal plane texture of Tl-1223 deposits prepared b y spray pyrolysis are observed to depend on the size of the x-ray beam . Furthermore, most grain boundaries were found from transmission elec tron microscopy to have small misorientation angles. It is concluded t hat although overall the basal plane orientations are nearly random, t here is a high degree of local texture indicative of colonies of simil arly oriented grains. The spread in a-axis orientation within a colony is approximately 10-degrees-15-degrees. Intercolony conduction, it is suggested, may be enhanced by a percolative network of small-angle gr ain boundaries at colony interfaces.