Cation substitution studies in YBa2Cu3O7-d structure

This paper reports on the suppression of superconductivity by the substitution of divalent cations such as Sr or Ca at Y and Ba sites in YBa2Cu3O7-d and the substitution of Pr for La in LaCaBaCu3O7-d that has been examined by ac susceptibility and infra-red spectroscopy. The latter has been found to be particularly useful in obtaining information at the microscopic level regarding the influence of substitution at the planes and at the chains. The studies give support for the model of enhancement of superconductivity by charge fluctuations in the chains. The systematics of the changes in the electrical by charge fluctuations in the chains. The systematics of the changes in the electrical resistivity in La1-xPrxCaBaCu3O7-d is examined in terms of the percolation models and the existence of a minimum sheet resistance for superconductivity. The role of the various substituents in stabilizing the structure and also in the mechanism for superconductivity is examined in terms of a model for the structure of the superconducting AmCunOy copper oxides on the basis of AX3 close-packing and the uniaxial magnetic interaction model