Proximity effect in Ag-Pb alloys
The superconducting properties and the microstructure of the Ag<sub>100-x</sub>Pb<sub>x</sub> alloys, 1 ≤ x ≤ 5, prepared by rapid quenching from the liquid state with and without subsequent heat treatments, have been studied. The x-ray diffraction measurements show that s...
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| Format: | Others |
| Language: | en |
| Published: |
1975
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| Online Access: | https://thesis.library.caltech.edu/8577/2/Sun_yse_1975.pdf Sun, Yen-Sheng Edmund (1975) Proximity effect in Ag-Pb alloys. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/eqtc-vh77. https://resolver.caltech.edu/CaltechTHESIS:07212014-154147234 <https://resolver.caltech.edu/CaltechTHESIS:07212014-154147234> |
| Summary: | The superconducting properties and the microstructure of the
Ag<sub>100-x</sub>Pb<sub>x</sub> alloys, 1 ≤ x ≤ 5, prepared by rapid quenching from the
liquid state with and without subsequent heat treatments, have been
studied. The x-ray diffraction measurements show that supersaturated
solid solutions of Pb in Ag can be obtained up to 3.2 at.% Pb as
compared to less than 0.1 at.% Pb at equilibrium. It was found that
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 theory
developed for the case of layer structure can be extended to three dimensions
to explain the critical current versus temperature behavior.
The critical current versus field behavior of these alloys can be explained
by the modification of the Josephson effect. Combining these
results together with the critical magnetic field measurements and the
microstructure studies of the alloys, it can be 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 in this investigation 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<sup>-5</sup> °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. |
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