HIGH-FIELD SUPERCONDUCTIVITY IN RAPIDLY QUENCHED Ge-(Pb, Bi, Sn) ALLOYS.

Rapidly quenched Ge-based alloys containing insoluble Pb, Bi and Sn have been found to exhibit superconducting behavior, particularly a markedly enhanced upper critical field H//c//2 which is higher than the highest value (15. 0T at 2. 0K) of commercial Nb-Ti superconducting alloys. The rapidly quenched structure consists of cubic-Ge and fcc-Pb for Ge-Pb alloys, cubic-Ge and epsilon (Pb-Bi) phases for Ge-Pb-Bi alloys; and cubic-Ge and Pb together with tetragonal Sn for Ge-Pb-Sn alloys. The Pb, epsilon (Pb-Bi) and Sn second phases all lie preferentially and discontinuously along the grain boundaries of the Ge matrix, in addition to their transgranular precipitation observed. The remarkable enhancement of H//c//2 is interpreted as due mainly to a significant decrease of the coherence length which results from a large reduction of the effective mean free path of the electrons.