We report on the application of the Resistively Shunted Junction (RSJ) model to granular high T C superconductors. Some derived predictions of the RSJ model are applied to a set of superconducting granular samples which can be considered as a network of Josephson junctions. The investigated samples belong to both hole-doped Y1-xPr xBa2Cu3O7-delta (x = 0.0, 0.35, and 0.45) and the electron-doped Sm2-xCe xCuO4-delta (x = 0.18) systems which display the so-called double resistive superconducting transition. We have performed several transport measurements in these compounds including temperature and magnetic field dependence of the electrical resistance, R(T,H), and I-V characteristics. Several aspects of the I-V characteristics were quantitatively well described by the RSJ model. The combined results strongly suggest that dissipation in granular superconducting samples is a natural consequence of the normal current flowing in parallel with the supercurrent current.

We have measured transport properties at low temperatures for the granular Sm1.82Ce0.18CuO4-delta samples belonging to the family of electron-doped superconductors. The effect of applied electrical current on the resistive behavior is investigated. The experimental data are analyzed using a modified form of the theory for a field-tuned superconductor-insulator transition in 2D superconductors. The results suggest a possible electrical-current driven superconductor-insulator transition.

This work presents a study of structural and magnetic properties of the Ba2Cu3O4Cl2 (Ba2342) compound. Doped samples with K or Sr in the Ba site and Zn or Mg in the Cu site of the Ba2342 were prepared using a solid state diffusion method. They were characterized by X-ray powder diffractometry, scanning electron microscopy and dc-magnetization. Samples with Ba2342 composition presented tetragonal structure of the I4/mmm space group when heat-treated at 750ºC. A structural transition was observed when the samples were doped with Zn or Mg or heat-treated at 700ºC. dc-Magnetization measurements performed in SQUID showed the existence of diamagnetic signal. A difference of the magnetic moments measured at zero field cooled (ZFC) and field-cooled (FC) procedures was observed suggesting the existence of localized superconductivity in this oxychloride system.