Preparation of nickel-based amorphous alloys with finely dispersed lead and lead-bismuth particles and their superconducting properties

The application of the melt-quenching technique to Ni-Si-B-Pb, Ni-P-B-Pb, Ni-Si-B-Pb-Bi and Ni-P-B-Pb-Bi alloys containing immiscible elements such as lead and bismuth has been tried and it has been found to result in the formation of a new type of material consisting of fine fcc Pb or hcp (Pb-Bi) + bct X(Pb-Bi) particles dispersed uniformly in the nickelbased amorphous matrix. The particle size and interparticle distance were 1 to 3 and 1 to 4 µm, respectively, for the lead phase, and less than 0.2 to 0.5 µm and 0.2 to 1.0 µm for the Pb-Bi phase. The uniform dispersion of such fine particles into the amorphous matrix was achieved in the composition range below about 6at% Pb and 7at% (Pb + Bi). Additionally, these amorphous alloys have been found to exhibit a superconductivity by the proximity effect of f c c Pb or (Pb-Bi) superconducting particles. The transition temperatureT _c was in the range 6.8 to 7.5 K for the Ni-Si(or P)-B-Pb alloys and 8.6 to 8.8 K for the Ni-Si (or P)-B-Pb-Bi alloys. The upper critical fieldH _c2 and the critical current densityJ _c for (Ni_0.8 P_0.1 B_0.1)₉₅ Pb₃ Bi₂ at 4.2 K were, respectively, about 1.6T and of the order of 7 X 10⁷ A m^–2 at zero applied field. Melt quenching of amorphous phase-forming alloys containing an immiscible element has thus been demonstrated, enabling us to produce amorphous composite materials exhibiting unique and useful characteristics which cannot be obtained in homogeneous amorphous alloys.