Weak link effects on the electrical properties of YBaCuO-CuO random composites

We report experimental data on the resistive transition of granular superconductive composites made of YBaCuO grains sintered in a CuO matrix as a function of temperature and grain concentration. The grain concentration dependence of the sample resistivity at constant temperature may exhibit two percolation transitions: a poor conductor-to-good conductor transition, which is present at every temperature, and a good conductor-to-superconductor transition below the grain superconducting transition temperature. We show that the temperature dependence of the superconductive critical concentration gives informations on the probability function describing the weak superconductive link transition to the normal state.