Comparative Study of Structural and Superconducting Properties of Ni-Substituted and NiO-Added YBa₂Cu₃O₇-δ Superconductors

Abstract

This study investigates the structural and superconducting behavior of YBa₂Cu₃O₇-δ (YBCO) superconductors doped with nickel through two distinct approaches: substitutional doping at the yttrium site and physical addition of NiO nanoparticles. Polycrystalline samples of Y(1-x)NixBa₂Cu₃O₇-δ and (YBCO)₁₋ₓ(NiO)ₓ with x ranging from 0.02 to 0.10 were synthesized using the solid-state reaction method. The crystal structures were characterized by X-ray diffraction (XRD), while superconducting transition temperatures (Tc) were determined through AC susceptibility measurements. XRD analysis confirmed the orthorhombic phase of YBCO for all Ni-substituted samples up to x = 0.06, beyond which slight peak broadening indicated lattice distortion and microstrain. In contrast, NiO-added samples exhibited secondary NiO phases at the grain boundaries, increasing with NiO concentration. AC susceptibility measurements revealed that substitutional Ni doping resulted in a gradual reduction of Tc due to magnetic pair-breaking effects and oxygen stoichiometry variations, while NiO addition caused severe suppression of superconductivity at higher concentrations by disrupting intergranular coupling. The results demonstrate that Ni substitution mildly modifies intrinsic superconducting properties, whereas NiO addition significantly deteriorates intergranular connectivity. Controlled substitutional doping is therefore more effective in tailoring YBCO properties for enhanced superconducting performance.