Effect of the Ba vacancy on the flux pinning in YBa x Cu 3 O 7-δ system

Abstract

A series of Y123 single phase samples with various Ba vacancy concentration was prepared by making their Ba contents deviate from the stoichiometric composition. The measurements of their structure, superconductivity and flux pinning behaviour were systematically carried out. It is found that, compared with YBa2Cu3O6.96 sample, the strength of the flux pinning in YBaxCu3O7-δ (1.8 ≤ x<2.0) samples is increased, and that there is an optimum value of Ba vacancy concentration for the maximum flux pinning force density. The possible origin of the flux pinning centers to determine the flux pinning behavior at higher field is discussed in detail. We suggest that the flux pinning effect at lower field may stem from the interaction between the vortex and the surfaces of grains, and that the flux pinning mechanism at higher field belongs to the core interaction.