Effect of submicron-sized AI₂O₃ inclusions on the superconducting order parameter fluctuation in YBa₂Cu₃0_7-δ superconductor

The effect of submicron-sized AI₂O₃ particle addition on the crystal structure and superconducting properties of YBa2Cu307-d ceramics was systematically studied. A series of 1-x(YBa₂Cu₃O_7-δ) + x(AI203)samples(x=0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6wt.%) were prepared using the solid state reaction method. The microstructure and the morphology of the polycrystalline samples have been characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) technique. The crystal lattice parameters and the orthorhombicity were decreased slightly with AI203addition. No change in the structural symmetry state was obtained. Morphology of the surface of pure samples reveals a considerable number of randomly oriented and dean grain boundaries. While in the composites, grain boundaries were filled with submicron-sized particles with enionged size. With the increase of AI₂O₃ addition, the superconducting transition temperatures (T_c) determined by standard four-probe method was decreased and dropped sharply with higher alumina content. Excess conductivity fluctuation analysis using Asiamazov-Larkin (AL) model fitting reveals transition of two dominant regions (2D and 3D) above T_c. The decrease in 2D-3D crossover temperature (TLD) (Lawerence-Doniach temperature) in the mean field region has been observed as a consequent dominance of 3D region to increase in wt.% of AI203in the composite.