Excess Conductivity of High-Temperature Superconductors Polycrystalline $Y_3Ba_5Cu_8O_{18\pm \delta }$ Doped with $TiO_2$ Nanoparticles

Abstract

Syntheses of the $Y_3Ba_5Cu_8O_{18\pm \delta }$ (noted Y-358) +x wt.% TiO₂ (x = 0.00, 0.10, 0.30, 0.50 and 0.60 wt%) bulk superconducting material are prepared by the standard solid-state reaction process. Then, systematic electrical conductivity fluctuation in normal and superconducting state analyses on the samples is reported. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to systematically assess stage formation and microstructures of the samples. XRD with the Rietveld refinement procedure showed that by cumulating the amount of TiO₂ nanoparticle into Y358 substance, the crystal lattice constants altered slightly and the orthorhombicity reduced compared to the pure sample. The impact of TiO₂ adding upon the superconducting characteristics with critical temperatures T_c analysis showed that as the inclusion of TiO₂ nanoparticles content increases the critical temperatures are enhanced for all of the doped samples. Evaluations of excess conductivity fluctuation were conducted by Aslamazov–Larkin (AL) model. Inside the grains, dimensional fluctuation is depending on the Lawrence–Doniach (LD) temperature named $T_{LD}$. This parameter ($T_{LD}$) was increased in the mean-field area by rising TiO₂ in Y358 substance compared to the non-added sample. However, analysing the excess conductivity based on the AL concept leads to the determination of thermodynamic fluctuation and some parameters values such as the critical temperature $(T_{c\ zero})$, coherence length $\xi _c(0)$, super-layer length d, critical magnetic fields $B_{c1}(0)$, $B_{c2}(0)$ and critical current density $J_c(0)$. These parameters which are significant by the TiO₂ nanoscale doping show that the theory outlined in the chapter “Excess conductivity model” is sufficient to describe our results.