Microwave studies of superconducting two-phase In-Sn

The variation of surface resistance with temperature and composition was determined for the indium-tin alloy system. Measurements made at 3 GHz enabled small inclusions of phases to be detected. Typically two transitions were seen corresponding to the eutectic and proeutectic constituents of the alloys. Between these transitions the surface resistance hardly changed with temperature. The flatness and mean value of the surface resistance in this temperature range were found to vary with the alloy's composition and the annealing conditions. Annealing was also found to affect the width of the superconducting transitions. Explanations for the results are suggested in terms of the flow of current in such systems and the proximity effect. Evidence was seen of a third transition under some annealing conditions. This extra transition may be explained by altering the β-phase boundary or adding a new intermediate phase to the present phase diagram. It is suggested that the γ-phase should begin at about 72 at.% tin rather than that presently accepted. (author)