Structure and properties of an intragranular weak link in Bi2Sr2CaCu2O8+x single crystals

Coupled magneto-optic imaging, four-point probe electrical characterization and transmission electron microscopy (TEM) of Bi2ST2CaCu2O8+x (2212) singl e crystals grown by directional solidification has revealed the presence of extensive, lamellar defects that lie parallel to the (010) planes of the s tructure. These defects block the supercurrent over areas that can reach hu ndreds of micrometers squared. Diffraction-contrast and high-resolution TEM revealed sheet-shaped defects that lie parallel to the (010) plane and in which the wavelength of the incommensurate modulation is perturbed. These l amellae are a few nanometers wide and, extends to tens to hundreds of micro meters on the (010) plane. The approximate doubling of the wavelength of th e incommensurate modulation within these lamellae indicates severe oxygen d eficiency. High-spatial-resolution X-ray spectroscopy indicates that the de fects are also Ca deficient. These macroscopic defects which are common in directionally-solidified 2212 single crystals, must be recognized in the in terpretation of single and synthetic bicrystal data, and may play a role in determining the percolative current path in bulk-scale 2212 materials. (C) 2001 Elsevier Science B.V. All rights reserved.