Abstract
The superconducting transition temperature and the critical current density of a splat-quenched Cu-0.4 at%Nb alloy were measured after age-treatments and the structure of some samples was observed by transmission electron microscopy. The results obtained are summarised as follows.
(1) In the samples as splat-quenched and aged at a relatively low temperature, the size of the precipitates (Nb particles) is small (<0.05 μm) and the superconductivity does not appear above 4.2 K. But after aging at 700°C for 4 hr, large precipitates (0.1∼0.2 μm) are observed and then the superconductivity appears above 4.2 K.
(2) The highest TC observed is 5.8 K when the sample is aged at 900°C for 4 hr, and the highest JC is about 95 A/cm2 when it is aged at 800°C for 4∼8 hr.
(3) The transition temperature TC and the critical current density JC of this sample show strong dependences on the size and the spacing of the Nb-precipitates. Therefore, it is considered that the superconductivity in this alloy is due to the proximity effect of Nb particles which precipitate on the grain boundaries.
