EFFECTS OF SUBSTITUTION FOR CU IN CUO2 PLANES WITH DOPANTS OF DIFFERENT ELECTRON CONFIGURATION IN YBA2CU3O7

The effects of substitution for copper in the system YBa2Cu3-xMxO7-y, with M = Ni, Zn and Ni1/2Zn1/2, and 0 less-than-or-equal-to x less-than-or-equal-to 0.5, have been studied with respect to its superconducting transition temperature, hole concentration, electronic transport properties in the normal state and structure parameters. The results strongly indicate that the band filling. the excess of holes, and electron localization due to the destruction of the integrity of the CuO2 planes are not the predominant factors for the suppression of T(c) in the case of substitution for Cu(2). Semi-quantitative analyses reveal that the Zn and Ni ions act as impurity scattering centres with a radius of scattering cross larger than the average Cu-O bond length of the CuO2 planes, which directly destroys the superconducting path in CuO2 Planes and decreases the superconducting energy gap. This may be the main reason for the suppression of superconductivity.