Effect of K substitutions on structural and superconducting properties in Bi-Pb-Sr-Ca-Cu-O (BPSCCO) system has been investigated. Bulk Bi1.6Pb0.4Sr2-xKxCa2Cu3O10+d (where x = 0.00; 0.04; 0.08 and 0.1) samples were fabricated by using the solid-state reaction method. Structural properties of the samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) measurement. All samples showed co-existence of  Bi-2223 and Bi-2212 superconducting phases. Interestingly, a formation of the Bi-2223 was decelerated and that of the Bi-2212 was accelerated with increasing K content (x). Superconducting properties of the samples were characterized by using temperature dependences of resistance and field dependences of magnetization data. Both onset and offset transition temperatures were found to decrease, those were correlated to the decreases in residual resistance ratio (RRR). The 65 K magnetization curves of K- substituted samples were enlarged in comparison with that of the pure one. Enlargements of the magnetization curves were possibly attributed to the appearance of additional point-like defects generated by substitutions of K into Sr site. Keywords: BPSCCO, substitutions, flux pinning, defects.

This paper studies the effects of the sintering temperature on crystal structure, critical temperature (Tc) and excess conductivity of Bi-Pb-Sr-Ca-Cu-O (BPSCCO) system. Bulk BPSCCO samples were fabricated by the solid-state reaction method. Four different temperatures of 835 °C, 840 °C, 845 °C, and 850 °C were applied to sinter four different samples. The crystal structure of the samples was investigated through X-ray diffraction measurements (XRD) and scanning electron microscopy (SEM). Superconductivity of the samples was analyzed by the temperature-dependent resistivity measurement. The experimental results showed the existence of both Bi-2223 and Bi-2212 phases in all samples. Quantitatively, the volume fraction of the Bi-2223 phase was found to increase from 53.56% to 75.97%, and the average grain size of Bi-2223 phase was observed to enlarge from 57.95 nm to 86.50 nm as the sintering temperature increased from 835 °C to 850 °C. In addition, the excess conductivity analyses based on the theory of Aslamazov - Larkin (AL) and Lawrence - Doniach (LD) showed decreases in the coherence lengths (ξc(0)) from 1.957 Å to 1.565 Å and the effective inter-layering spacing (d) from 79.7 Å to 64.5 Å. Meanwhile, the interlayer coupling strength (J) between two CuO2 planes was estimated to increase from 0.00083 to 0.00137. These results might be evidence to conclude that the increasing of the sintering temperature obviously improves the superconductivity in the BPSCCO system.