Morphology of growth of Bi₂Sr₂CaCu₂O₈ single crystals

A good correlation of twins on the basal surface of flux-grown Bi₂Sr₂CaCu₂O_X (BSCCO) single crystals with surface, growth steps is observed, the b-axis being perpendicular to the steps and, thus, parallel to the growth direction. It is found that mono-twin BSCCO single crystals produced by the travelling solvent floating zone method also grow preferentially along b, i.e. nearly perpendicularly to the boule axis, contrary to the common belief. This new understanding of the morphology of growth explains the nature of major defects in these crystals, which considerably change their measured superconducting properties, in a different way.