A study of superconducting (Y1-xCax)Ba2Cu3Oy

We have investigated the effects of hole doping in the Y-Ba-Cu-O system by substituting calcium(II) in the Y(III)-site. We have analysed the resistivity, paraconductivity, interlayer coupling strength (J) as a function of dopant concentration. T-c and J are found to decrease with increasing calcium content. We have also studied surface binding energies of various components in a Ca doped sample through secondary ion mass spectrometry (SIMS). The binding energy of CuO in a CuO2 sheet does not increase as compared to that in undoped YBCO, indicating that the extra hole doped in the Y site does not bring positive charge to the conducting CuO2 layer. Doping of calcium perhaps destroys the ordering of oxygen in the Cu-O-Cu chain, which affects superconductivity.