Percolation behavior of the normal-state resistivity and superconductivityof the YBa2Cu3O7-delta-Ba2GdNbO6 composite system

The percolation behavior of the normal-state resistivity and superconductiv ity of the YBa2Cu3O7-delta-Ba2GdNbO6 composite system were studied by X-ray diffraction and temperature-resistivity measurements. No detectable chemic al reaction was observed between the YBa2Cu3O7-delta superconductor and the ceramic insulator Ba2GdNbO6, even after severe heat treatment above 950 de grees C. The normal-state and superconducting percolation threshold values were found to be 17 vol.% and 30 vol.% of YBa2Cu3O7-delta respectively in t he YBa2Cu3O7-deltaBa2GdNbO6 composite system. The values obtained for the c ritical exponents describing the normal-state pecolation behavior of the sy stem matched fairly well with the theoretically expected values for an idea l metal-insulator composite system.