Precipitation and Superconductivity in Lead-Tin and Lead-Cadmium Alloys

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Abstract
The effects of precipitation from solid solution on the superconducting properties of lead‐tin and lead‐cadmium alloys have been studied by magnetization measurements at 4.2°K. Microstructural changes have been followed by optical and electron microscopy. These alloys as‐quenched are superconductors of the second kind, their upper critical fields enhanced by quenched‐in solute. At various stages in the precipitation process, the upper critical field continues to be determined primarily by the remanent solute. Magnetic hysteresis and trapped flux result from the interaction between precipitates and the flux filaments of the mixed state, a given precipitate distribution causing much more flux trapping if the matrix is a superconductor of the second kind than if it is a superconductor of the first kind. Several instances are seen where superconducting magnetization measurements yield useful metallurgical information.