INTERPLAY OF ELECTRONIC AND STRUCTURAL FEATURES IN ZN-DOPED AND FE-DOPED YBCO

In order to discover the effects of oxygen ordering and carrier concen tration on YBCO superconductivity, Zn- and Fe-doped systems were inves tigated as a function of dopant concentration and of oxygen stoichiome try, and with respect to resistive characteristics, bulk symmetry and oxygen microdomain ordering. The pair-breaking imputable to Zn substit ution was found to be very effective on T-c, but not related to any st ructural modification or oxygen stoichiometry reduction. On the contra ry, the Fe induced effects were observably perturbing the oxygen order ing and consequently reducing T-c. The analysis of the T-c versus oxyg en stoichiometry plots relevant to the doped compounds suggests that d ifferent mechanisms drive the T-c reduction, depending on the site of substitution: electronic pair-breaking is dominant in Cu2 substituted systems (like Zn-doped YBCO) at the CuO2 conduction planes, while carr ier concentration reduction is more effective in Cu1 substitution case s (like the Fe-doped one), where doping occurs at the CuO reservoir la yers.