Properties of Y Ba2 Cu3 O7-δ-Ag superconductors prepared by the citrate method

Y Ba2 Cu3 O7-δ (123) ceramic superconductor and YBa2 Cu3 O7-δ - Ag composite superconductors have been prepared by the citrate method. Microstructural analysis has been done by X-ray diffractometry and optical ceramography. The superconducting behaviour has been studied by 4-probe dc resistivity in the 77 K - 140 K temperature range. Silver percolation in the ceramic matrix was studied by electrical resistivity measurements at room temperature; the percolation threshold was found to be approximately 25 vol% (35.5 wt%) Ag. Specimens with silver addition showed improvement in the flexural strength of the 123 compound. The main results show that the critical temperature does not depend on the silver content in the composite specimens, and that approximately 3 wt% (1.8 vol%) Ag doping yields an optimized composite superconductor from the microstructural point of view, with platelet-like grain shapes. (author)