Enhancement of Pinning Role by Nonstoichiometry in YBa2Cu3O7−y Superconductors

Considerably improved flux pinning and critical current density Jc 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−xBa2Cu3O7−y can be regarded as (YBa2Cu3)1−xO7−t(Ba2Cu3) x Ot−y or (YBa2Cu3O7−z)(□ x YOz−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 Jc 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.