Enhancement of pinning role by nonstoichiometry in YBa2Cu3O7-y superconductors

Abstract

Considerably improved flux pinning and critical current density J c values have been achieved in Y-deficient Y-123 superconductors by directional solidification in air. In comparison with the regular Y-123 composition, Y-deficient one also has an orthorhombic structure and Y-123 main crystal phase remains in it. Whereas with the shortage of Y, Y1−x Ba2Cu3O7−y can be regarded as (YBa2Cu3)1−x O7−t(Ba2Cu3) x O t−y or (YBa2Cu3O7−z )(□ x YO z−y ), so there may develop several kinds of microstructure defects as pinning sites in the system, such as highly dense, fine-scale, and faultlike defects, as well as localized superstructure, which are able to induce the increasing in flux pinning and J c values in higher external magnetic fields. This kind of simple nonstoichiometric route could lead to a commercial technique for flux-pinning enhancement in Y-123 bulk materials.