Defect formation in the intermediate layers of YBa₂Cu₃O₇₋δ superconductors depending on oxygen сontents

Abstract

In YBa₂Cu₃O₇₋δ superconductors with 0≤δ<0.6 the defect formation in the intermediate layers depending on oxygen content was revealed under γ-irradiation with doses 8-250 kGy. In YBa₂Cu₃O₇ the subthreshold creation of Ba, Cu1, O1 defects, which give rise to lowering of the annihilation rate of positrons and lattice parameter c, disorder of Cu-O chains, dominates. The defect formation is weakened with δ growth. In YBa₂C₃3O₆.₇ superconductor the subthreshold pushing out of atoms occurs at low temperatures and in O1→O5 transitions, while in compounds with δ>0.3 the subthreshold defect formation in the intermediate layers is not observed. The subthreshold defect formation is related to the Coulomb ejection of atoms from the lattice sites in the field of the weakly damped low-frequency collective excitations enhanced by irradiation in YBa₂Cu₃O₇₋δ superconductors with δ≤0.3.