Effect of Josephson Medium Under Tunneling in Bi-Sr

Tunneling characteristics of high-T_c oxide superconductor Bi-Sr-Ca-Cu-O have been measured in the wide bias voltage and temperature range. Near zero bias voltage tunneling conductivity σ (U) is expressed by the U^1/2 at low temperature, which goes to the linear one at U > 100 mV. Background conductivity metaloxide is determined by Shottky barrier on surface high-T_c. It has been found that the peaks of σ (U) curves for low-ohmic contacts are well described theoretical model of destruction of superconductivity of the intergranular weak links. Parameters of these links are estimated. Zero bias anomaly conductivity peaks are explained by breakdown weak links with small critical current.