Structure related superconducting properties in oxygen-chainequalized and order-stabilized pairs of 123 copper oxides

The results of resistive Tc and electron diffraction measurements, comparatively performed on oxygen-chain-equalized polycrystalline pair-samples of YBa2 Cu3O6+x, are reported. The samples were prepared from the full/empty oxygen-chain [Cu(1)Ox]x 1/[Cu(1)Ox]x 0 stoichiometry end terms long time equilibrated under vacuum at low temperature and order-stabilised in the appropriate temperature-composition domain of existence of OII and OIII superstructures. Evidence for Tc-singularities and Tc-splittings, structurally related with common and different superstructure reflections in the electron diffraction patterns, is given. The singularity appears at characteristic values of oxygen content in the pair-samples where superstructures have been found or predicted by theory. The observed phenomena are of intrinsic nature and can be interpreted, in the framework of the charge transfer model, as associated to equivalent (Tc-singularity) or non-equivalent (Tc-splitting) hole density contributions to the Cu(2)O2 planes from equivalent or non equivalent oxygen-vacancy ordering in the basal Cu(1)Ok plane.