A comparative study of enhancements of critical temperature in Bi-Pb-Sr-Ca-Cu-O superconductors

Abstract

In this work, the effects of sintering temperature and Na subtitution on zero critical temperature (Tc,0) in Bi-Pb-Sr-Ca-Cu-O superconductors were investigated. The Bi1.6Pb0.4Sr2Ca2-xNaxCu3O10+d bulk samples with x = 0.00 and 0.05 (BPSCCO) were prepared by using the solid state reaction technique at elevated sintering temperatures of 840 and 850oC. To examine the improvements of structural and superconducting properties of the BPSCCO samples, the X-ray diffraction (XRD), scanning electronic microscope (SEM) and DC resistance versus temperature (R-T) measurements were carried out. The experimental findings exhibit a co-existence of the high Tc (Bi-2223) and low Tc (Bi-2212) phases in all samples. The estimated volume fraction of the Bi-2223 phase was increased from 71.4 to 75.7%, and the average size of the Bi-2223 grains was enlarged from 4.5 to 9.8 mm as changing the sample preparation conditions. The improved connectivities between the Bi-2223 grains were also obtained by quantitively analyzing the relation between Tc,0 and residual resistance ratio (RRR). These improvements were likely to be reasons for the enhancements of Tc,0 in the BPSCCO samples.