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.

Este trabalho aborda a preparação de pós cerâmicos de zircônia (ZrO2) estabilizada com um concentrado de óxidos de Ítrio e terras raras (OTR). O objetivo principal deste trabalho é a obtenção de eletrólitos sólidos de zircônia para aplicação em sensores de oxigênio. O método de preparação adotado foi o de co-precipitação química dos respectivos hidróxidos em meio amoniacal (NH4OH). Foram preparadas amostras variando a concentração de OTR, entre 10 e 35% em massa. São apresentados e discutidos os resultados de análise de fases por difração de raios X, auxiliada por um programa computacional e um modelo matemático para cálculo dos parâmetros de rede, análises químicas, termo-gravimétrica e termo-diferencial (ATG/ATD).

This work reports the preparation of ceramic zirconia powders (ZrO2) stabilized with a concentrate of Yttrium and rare earth oxides (OTR). The main objective of this work is to obtain solid electrolytes of zirconia for application in oxygen sensors. The preparation method was by chemical coprecipitation of the respective hydroxides with ammonia (NH4OH). Samples were prepared changing the concentration between 10 and 35 wt.% OTR. Phases analysis by X-ray diffraction, aided by a program computational and a mathematical model for calculation of lattice parameters, chemical, thermogravimetry, and differential thermal analysis (TGA/DTA) are presented and discussed.