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, Y_1−x Ba₂Cu₃O_7−y can be regarded as (YBa₂Cu₃)_1−x O_7−t(Ba₂Cu₃) _x O _t−y or (YBa₂Cu₃O_7−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.