SUBSTITUTION OF SN IN THE SUPERCONDUCTING BI-PB-SR-CA-CU-O SYSTEM

X-ray powder diffraction, magnetic susceptibility and electrical resistivity measurements have been used to investigate the effect of Sn substitution in the Bi1.7Pb0.3Sr2Ca2 (Cu3-xSnx)1.2Oy system for different values of Sn concentration x (0 less-than-or-equal-to x less-than-or-equal-to 1.33). The substitution of Sn is found to decrease the superconducting volume fraction of the 2223 phase. The 2212 phase is enhanced until it reaches a maximum at x = 0.67. The system has a complete 2212 phase at x = 0.88. An increase in the normal-state resistivity with a corresponding suppression of the temperature at which the resistivity goes to zero is observed with increasing x for the samples which are superconducting. The substitution of Sn probably causes a spatial disorder in the CuO2 planes, which in turn enhances the Coulomb interaction. Samples with x greater-than-or-equal-to 1.0 are found to be insulating.