Dislocations and Flux Pinning inYBa 2 Cu 3 O 7-δ

Abstract

Bulk YBa₂Cu₃O_7-δ superconductors, under certain processing conditions such as melt texturing, exhibit a very high dislocation density of 10⁹ to 10¹⁰ per square centimeter. In addition, the density of low-angle grain boundaries in such samples can be significantly increased (to less than 700-nanometer spacing) through a dispersion of submicrometer-sized Y₂BaCuO₅ inclusions. These defect densities are comparable to those in high critical current thin films as revealed through scanning tunneling microscopy, and yet the critical current densities in the bulk materials (at 77 kelvin and a field of 1 tesla for example) remain at a 10⁴ amperes per square centimeter level, about two orders of magnitude lower than in thin films. The results imply that these defect density levels are not significant enough to explain the difference in flux pinning strength between the thin film and bulk materials. The observation of spiral-like growth of the superconductor phase in bulk Y-Ba-Cu-O is also reported.