Conductivity features of the nanomodified HTSC structures

The transport characteristics of nanostructures consisting of microcrystalline YBa₂Cu₃O_7-δ powder and nanopowder of the same composition have been studied in the nanosecond duration interval of the pulse voltages applied to the nanostructure. An increase in the critical temperature T_c of the transition to the superconducting state was established to occur at the 20% nanopowder content. The obtained experimental data was interpreted in terms of the percolation theory. This theory holds that the optimal nanopowder content in the nanomodified material causes a rise of the maximum number of micropowder-nanopowder Josephson’s contacts. An increase in the structure porosity when the content falls off from the optimum, leads to a break-down of a percolation cluster and to a decrease in the T_c value; moreover, the temperature range where the transition to the superconducting state takes place, spreads.