Microstructure and superconducting properties of melt-quenched insoluble Al-Pb and Al-Pb-Bi alloys

Abstract

In order to obtain aluminium-based superconducting alloys including finely dispersed lead or Pb-Bi particles, the application of the melt-quenching technique has been tried for Al-Pb, Al-Si-Pb and Al-Si-Pb-Bi alloys containing immiscible elements such as lead and bismuth. It has been found to result in the preparation of superconducting materials consisting of fcc Pb or h c p ε(Pb-Bi) particles dispersed finely and densely in the aluminium-based matrix in each composition range below about 2 at % Pb for Al-Pb alloys and 5 at % Pb or (Pb + Bi) for (Al_0.9 Si_0.1)_100−x Pb _x and (Al_0.9Si_0.1)_100−x (Pb_0.6Bi_0.4) _x alloys. The particle size and interparticle distance were ∼ 40 nm and 40 to 100 nm, respectively, within the grains, and ∼ 100 nm and below ∼ 30 nm, respectively, at the grain boundaries for the lead phase in Al₉₈ Pb₂ alloy. Particle size was ∼ 15 to 60 nm and interpartide distance 30 to 60 nm for the Pb- Bi phase in (Al_0.9 Si_0.1)₉₅(Pb_0.6 Bi_0.4)₅ Transition temperature,T _c was 4.16 K for Al₉₈Pb₂, 3.94K for (Al_0.9Si_0.1)₉₅ Pb₅ and 7.75 K for (Al_0.9Si_0.1)₉₅(Pb_0.6Bi_0.4)₅. The upper critical magnetic field,H _c2, and critical current density,J _c, for (Al_0.9Si_0.1)₉₅(Pb_0.6Bi_0.4)₅ were 0.22 T at 4.2 K and 1.67 × 10⁷ Am⁻²atzeroappliedheld and 4.2 K. The appearance of the superconductivity for the aluminium -based alloys was interpreted as due to the formation of superconducting percolation path along the tangled dislocations, sub-boundaries and/or grain boundaries where Pb and Pb-Bi phases precipitated preferentially.