The superconducting properties are reviewed on the melt-quenched alloys consisting of immiscible Pb, Al or Pb-Bi particles embedded in Cu- and Ni-based amorphous or cubic Ge matrix. The superconductivity of the duplex amorphous alloys containing Pb and Pb-Bi particles is investigated in the theory based on the proximity effect and has been interpreted to result from a homogeneous distribution of the superconducting particles in the amorphous matrix with an extreme dirtiness. Additionally, a remarkable enhancement of superconductivity was found to occur for Ge-rich alloys containing Al, Pb or Pb-Bi particles. The significant enhancement has been inferred as due to the decreases in the phonon frequency and the effective mean free path of electrons through the quenching-induced structural modification
