EXAFS studies of (Pb,Cd)1212 phase superconductor and (Bi,Cd)1212 phase compound

We synthesized (Pb,Cd)Sr-2(Y,Ca)Cu2O7+x phase superconductor. After substit ution of ph with Bi, the BiCd1212 phase shows no superconductivity. Althoug h previous EXAFS study has shown the local structure environment of the Cu is similar in both compounds, EXAFS results of Bi and Pb here demonstrate t hat sigma(2) of Pb-Oin-plane is larger than that of Bi-Oin-plane, whereas s igma(2) of Pb-O-apical is smaller than that of Bi-O-apical. The Sr shell fe atures are also different. It appeared that superconductivity needs some di sorder in carrier reservoir layer, which is due to the substitutional defec t caused by different ionic radii.