STRUCTURE RELATED SUPERCONDUCTING PROPERTIES IN OXYGEN-CHAIN-EQUALIZED AND ORDER-STABILIZED PAIRS OF 123 COPPER OXIDES

The results of resistive T-c and electron diffraction measurements, co mparatively performed on oxygen-chain-equalized polycrystalline pair-s amples of YBa2Cu3O6+x, are reported. The samples were prepared from th e full/empty oxygen-chain [Cu(1)O-x](x similar to)1/[Cu(1)O-x](x simil ar to 0) stoichiometry end terms long time equilibrated under vacuum a t low temperature and order-stabilised in the appropriate temperature- composition domain of existence of OII and OIII superstructures, Evide nce for T-c-singularities and T-c-splittings, structurally related wit h common and different superstructure reflections in the electron diff raction patterns, is given. The singularity appears at characteristic values of oxygen content in the pair-samples where superstructures hav e been found or predicted by theory. The observed. phenomena are of in trinsic nature and can be interpreted, in the framework of the charge transfer model, as associated to equivalent (T-c-singularity) or non-e quivalent (T-c-splitting) hole density contributions to the Cu(2)O-2 p lanes from equivalent or non equivalent oxygen-vacancy ordering in the basal Cu(1)O-k plane.