Comparative study of nano-sized particles CoFe₂O₄ effects on superconducting properties of Y-123 and Y-358

The effects of nano-sized CoFe₂O₄ particles (10 nm) addition on the structural and the normal state resistivity of YBa ₂Cu₃O₇ (noted Y-123) and Y₃Ba ₅Cu₈O₁₈ (noted Y-358) polycrystalline were systematically studied. Samples were synthesized in oxygen atmosphere using a standard solid state reaction technique by adding CoFe₂O₄ up to 2 wt%. Phases, microstructure and superconductivity have been systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical measurements ρ(T). XRD results reveal that the lattice parameters change for both Y-123 and Y-358 phases. SEM observations reveal that the grain size is reduced with increasing the content of CoFe ₂O₄. The measurements for the resistivity dependence of temperature show that the depression in superconducting temperature is more pronounced for CoFe₂O₄ addition in Y-358 compound than in Y-123 one. These results may be attributed to the existence of much more disorder due to a greater number of Cu sites to be substituted by Fe and Co in Y-358 compared to Y-123.