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Abstract This work investigates the effect of low-level Fe incorporation (x ≤ 0.009) in YBa 2 Cu 3 O 7−δ , nominally at the Y site, on the structural and superconducting properties. X-ray diffraction confirms preservation of the orthorhombic phase with subtle changes in lattice parameters, suggesting local distortions and modifications in oxygen ordering. Resistivity measurements reveal a two-stage superconducting transition associated with intragranular pairing and intergranular coherence, consistent with weak-link behavior in polycrystalline samples. A slight maximum in characteristic temperatures is observed at x ≈ 0.2–0.3%, followed by a decrease at higher Fe content. Magnetic measurements show a reduction of the diamagnetic response and irreversibility temperature with doping. The results indicate competition between weakened intergranular coupling and enhanced intragranular vortex pinning induced by Fe-related defects, highlighting a low-doping regime for tuning superconducting performance.
Fajardo et al. (Thu,) studied this question.