Superconductivity in a Ge-doped Bi-Pb-Sr-Ca-Cu-O system

The effect of the substitution of Ge in the Bi1.6Pb0.4Sr2Ca2Cu3-xGexOy system has been investigated by means of X-ray diffraction and electrical resistivity measurements. The volume fraction of the 2223 phase is found to decrease with increasing Ge concentration. The lattice parameter c of the 2223 phase decreases slightly with increasing Ge concentration. The onset of the superconducting transition is about 110 K for all samples. The temperature of zero resistivity, however, is suppressed with Ge substitution. The superconductivity of the 2212 phase is evident only for x=0.5. There is evidence of weak links between the grains. The ratio of the extrapolated residual resistivity to the normal-state resistivity increases with increasing Ge concentration indicating that the disorder in the system increases with x.