Excess Conductivity Study in Nano-CoFe2O4-Added YBa2Cu3O7−d and Y3Ba5Cu8O18±x Superconductors

We report electrical conductivity fluctuation analyses on YBa 2 Cu 3 O 7− d (noted Y-123) and Y 3 Ba 5 Cu 8 O 18± x (noted Y-358) polycrystalline samples added with nano-sized ferrite cobalt (CoFe 2 O 4 ) particles. Phases and microstructure have been systematically investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results reveal that the lattice parameters change for both Y-123 and Y-358 phases. SEM observations show that the grain size is reduced with increasing the content of CoFe 2 O 4 in the yttrium-based superconductor (YBCO) matrix The temperature dependence of electrical resistivity ρ ( T ) has been measured and the effect of addition of magnetic CoFe 2 O 4 in the paraconductivity region has been reported. The thermodynamic fluctuation is obtained by analyzing the excess of conductivity on the basis of the Aslamazov–Larkin theory. The coherence length, the effective layer thickness, critical magnetic fields, and critical current density are estimated. Superconducting parameters are affected by the nanoparticle addition, and results are discussed in relevance to the structural and microstructure differences between Y-123 and Y-358.