Bi1.7Pb0.3-xTbxSr2Ca 3Cu4Oy compounds (0.0?×?0.1) are synthesized by using the conventional high temperature melt quenching technique to study the influence of Tb substitution on their high-Tc superconducting properties. The effects of different Tb doping levels on the superconductor structure have been investigated by electrical resistance, magnetoresistance, scanning electron micrographs, and XRD measurements. It has been observed that, with increasing Tb3+ substitution for Pb 2+ the high-Tc Bi-(2223) phase gradually transforms into the low-Tc Bi-(2212) and Bi-(2201) phases. It should be pointed out that the low-Tc superconducting phases of Bi-(2212) and Bi-(2201) are formed for all the doping levels. The data suggest that with the increasing Tb3+ doping level the superconductivity in Bi1.7Pb 0.3-xTbxSr2Ca3Cu4O y system is suppressed due to the destruction of the phase coherence by pair-breaking effects, such as magnetic. The magneto-resistance results clearly demonstrate that with increasing magnetic field first the high-T c Bi-(2223) phase gradually diminishes and almost the low-T c Bi-(2212) phase remains, however, the trends indicate that at a reasonably high magnetic field the low-Tc phase will also be destroyed and hence the superconductivity will not be observed any more, as expected
