Effect of granularity and inhomogeneity in excess conductivity of YBa2Cu3O7−δ+xBaTiO3 superconductor

Synthesis of polycrystalline YBCO+xBaTiO3 (x=1.0, 2.5, 5.0) superconductor has been done and the effects of granularity and inhomogeneities due to inclusions of nano-BaTiO3 in excess conductivity are reported in this work. The phase formation, texture and grain alignments were analyzed through XRD and SEM techniques. SEM results reveal that the grain size is reduced and morphology is improved with the incorporation of nano-BaTiO3 particles. Superconducting order parameter fluctuation (SCOPF) studies on the electrical conductivity were investigated from the resistivity vs. temperature data in the experimental domain relatively above Tc. Log(Δσ) vs. log(ε) plots show that the 2D to 3D crossover temperature (TLD) that demarcates dimensional nature of fluctuation inside the grains is influenced by BaTiO3 incorporation in YBCO matrix. An upward shift of TLD in the mean field region has been observed as a consequent dominance of 3D region with increase in 1 wt% BaTiO3 in the composites as compared to higher inclusions. It has been analyzed that microscopic inhomogeneities produced as a result of diffusion of a fraction of Ti ions into the grains affect fluctuations in the excess conductive region. The interplay of microscopic inhomogeneities produced inside the grains and mesoscopic inhomogeneities in the grain boundaries on the excess conductivity has been explained in terms of thermal fluctuations for the composites.

Research highlights
► Superconducting order parameter fluctuation effects on YBa2Cu3O7−δ+xBaTiO3 composites.
► Effect of granularity and inhomogeneity in excess conductivity of YBCO with BaTiO3 inclusion.
► Intergrain coupling as weak links in granular superconductors to enhance transport properties.
► Structural and dimensional changes with inclusion of nano-BaTiO3 to the YBCO matrix.