Limit of superconductivity in silver/superconductor metal-matrix composites prepared with Bi–Pb–Sr–Ca–Cu–O ceramic powders

Abstract

Superconducting composite samples were prepared by sintering a mixture of metallic silver and Bi(Pb)–Sr–Ca–Cu–O powder in air. For Ag contents between 0 and ∼15 vol. %, the bulk critical temperature was depressed as much as 40 K, and the relative proportion of the 2223 phase with respect to the 2212 phase was decreased, compared to the pure sample. However, as the Ag content was increased to between 19 and 70 vol. %, critical temperatures above 100 K were measured by transport and ac susceptibility techniques, and the relative proportions of the phases were restored to that of the pure sample. The limit of bulk superconductivity was reached at 73 vol. % Ag where the bulk critical temperature was ∼85 K. For higher Ag contents bulk superconductivity was not observed. Our results also show that sintering in air of silver-clad tapes containing Bi(Pb)–Sr–Ca–Cu–O powder, either by itself or with silver powder, need not be detrimental to the final superconductive properties.