A CLOSE CORRELATION BETWEEN DISORDERS-DEFECTS AND SUPERCONDUCTING TRANSITION TEMPERATURE OF Bi1.6Pb0.4Sr2Ca2-xNaxCu3O10+δ SUPERCONDUCTORS

The enhancements of zero superconducting transition temperature (Tc,0) in Bi1.6Pb0.4Sr2Ca2-xNaxCu3O10+δ(BPSCCO) are reported. The BPSCCO samples (with x ranging from 0.00 to 0.06) were prepared by using the conventional solid state reaction technique. The properties of the samples were examined by using the X-ray diffraction (XRD), scanning electron microscopy (SEM), and the resistance versus temperature (R-T) measurements. From the XRD resuts, all samples revealed the orthorhombic structure, and the volume fraction of the Bi-2223 phase was varied as increasing x, and reached the maximum value of 82.72 % for x = 0.05 sample. Improvements of connectivity between the Bi-2223 grains in the Na-substituted BPSCCO samples were obtained by using the surface SEM images and a quantitive analysis of a correlation between Tc,0 and residual resistance ratio (RRR). A similar variation of Tc,0 of the samples as increasing x was observed. The highest Tc,0 enhancement of 107.5 K was obtained for x = 0.05 sample. Variations of the hole carrier concentrations in the CuO2 layers were investigated, which also showed the highest value achieved for x = 0.05 sample