Role of barium addition on the properties of bismuth-based superconductors

The effect of the addition of barium on the zero resistance temperature,T _c, of Bi_1.6Pb_0.4Sr_1.6Ca₂Ba _x Cu₄O _y ,x= 0.4, 0.5, 0.6, 0.8 and 1.6 was studied. The added barium had the effect of raisingT _c to a higher temperature region, although too much barium gave rise to semiconducting resistance temperature behaviour. X-ray diffraction analysis showed that as the barium concentration,x, increased from 0.4 to 0.8, a decrease in the lowT _c phase and peaks due to CuO and BaBiO₃ appeared, whereas an increase in the peaks due to the highT _c phase and BaCuO₂ were seen. Critical current densities were also measured in zero field at 77 K.