Crystallization-induced superconductivity in amorphous Ti-Ta-Si alloys

Amorphous alloys containing 0 to 40 at% Ta and 15 to 20 at% Si have been produced in the ternary Ti-Ta-Si system by rapidly quenching the melts using a melt-spinning technique. The amorphous alloys did not show any superconducting transition down to liquid helium temperature (4.2 K). However, a transition was detected above 4.2 K after inducing crystallization in these alloys by annealing at appropriate temperatures. The superconducting transition temperature, T _c, increased with increasing tantalum content and showed the highest value of 7.6 K for the Ti₄₅Ta₄₀Si₁₅ alloy annealed for 1 h at 1073 K. An upper critical magnetic field, H _c2 of 4.7×10⁶ Am^–1 at 4.2 K and a critical current density, J _c, of 1.5×10⁴ A cm^–2 at zero applied field and 4.2 K were recorded for this alloy. Detailed electron microscopic studies of the crystallization behaviour of the amorphous alloys established that a supersaturated solid solution of tantalum in -Ti with a bcc structure forms first, followed by the precipitation of the bc tetragonal Ta₃Si compound. Since Ta₃Si is not superconducting above 4.2 K, it has been concluded that superconductivity in the crystallized alloys is due to the precipitation of -Ti(Ta) solid solution.