PROPERTIES OF YBA2CU3O(7-DELTA)-AG SUPERCONDUCTORS PREPARED BY THE CITRATE METHOD

YBa2Cu3O7-delta (123) ceramic superconductors and YBa2Cu3O7-delta-Ag c omposite superconductors have been prepared by the citrate method. Mic rostructural analyses have been done by X-ray diffractometry and optic al ceramography. The superconducting behavior has been studied by 4-pr obe dc resistivity in the 77 K-140 K temperature range. Silver percola tion in the ceramic matrix was studied by electrical resistivity measu rements at room temperature; the percolation threshold was found to be approximately 25 vol% (35.5 wt%) Ag. Specimens with silver addition s howed improvement in the flexural strength of the 123 compound. The ma in results show that the critical temperature does not depend on the s ilver content in the composite specimens, and that approximately 3 wt% (1.8 vol%) Ag doping yields an optimized composite superconductor fro m the microstructural point of view, with platelet-like grain shapes.