Proximity effect in Ag--Pb alloys

The superconducting properties and the microstructure of the Ag/sub 100-x/Pb/sub x/ alloys (1 less than or equal to x less than or equal to 5) prepared by rapid quenching from the liquid state with and without subsequent heat treatments, were studied. X-ray diffraction shows that supersaturated solid solutions of Pb in Ag can be obtained up to 3.2 at. percent Pb. By suitable heat treatment, it is possible to vary the size and distribution of the Pb precipitates in the Ag matrix and reproducible superconducting properties in the alloy can be observed. The superconducting transition temperature of these samples can be qualitatively explained by the Silvert and Singh's theoretical calculation. The critical current versus field behavior of these alloys can be explained by the modification of the Josephson effect. It was concluded that the three-dimensional proximity effect is the main mechanism for the superconductivity in the Ag--Pb alloys. Based on the Hilsch empirical formula which was based on experimental results obtained on layer structures, the experimental data show that the electron--phonon--electron interaction in silver is attractive. The interaction parameter NV obtained is approximately 0.06, which would lead to a value of 10^{-5 0}K for the superconducting transition temperature of Ag. These values are in agreement with other determinations which were done on vapor-deposited metallic film sandwiches. Hence, the Hilsch empirical relation valid for layer structures is also valid in the three-dimensional case. Because the transition temperature and the critical current can be varied in a wide range by controlling the heat treatments, the Ag--Pb superconductors might have some useful applications. (author)