The characterization of bi-based ceramic superconductors by magnetic susceptibility measurements

The effects of addition of Niobium and Gadolinium on structural, magnetic and superconducting properties in Bi1,7-xPb0,3GdxSr2Ca2Cu3Oy and Bi1,7-xPb0,3NbxSr2Ca2Cu3Oy superconducting samples were investigated. The superconducting samples were prepared by conventional solid state reaction method. The investigation consisted of X-ray diffraction (XRD), scanning electron microscope (SEM), density measurements for structural characterization, surface morphology and phase analysis and ac susceptibility to determine the critical current density and hole concentration of the samples. In ac susceptibility measurements with Niobium addition, the critical onset temperatures were observed to be about 108, 105, 104, 105 and 100 K for samples Nb0, Nb1, Nb2, Nb3 and Nb4, and with Gadolinium addition, the critical onset temperatures were observed to be about 108, 77, 77, 72, and 70 K for samples Gd0, Gd1, Gd2, Gd3 and Gd4, respectively. XRD measurements show that high-Tc phase increases and low-Tc phase decreases with the Niobium substitution whereas high-Tc phase volume fraction decreases and low-Tc phase volume fraction dominates the system with increasing Gd addition. When Niobium addition was increased, the porosity decreases and grain connectivity of the samples were observed to improve and when Gd addition ratio was increased, surface morphology and grain connectivity of the samples were observed to degrade from SEM investigations. Density measurements are in line with SEM results. Keywords: AC susceptibility, XRD, SEM