Amorphous structure of the immiscible Fe1-y(Cu1-xAgx)yalloy system

Fe 1-y (Cu 1-x Ag x ) y alloys sputter deposited on liquid-nitrogen-cooled substrates have been investigated by X-ray diffraction and differential scanning calorimetry measurements. Although this ternary alloy system is of a typically immiscible type in the equilibrium state, a single BCC phase appears at the Fe-rich corner and a single FCC phase at the Cu- and Ag-rich corners, while an amorphous phase appears in the central concentration region. In the interference function of the ternary amorphous alloys, a broad first peak and splitting of the second and third peaks are detected, where the peak intensity is much weaker than those in the binary FCC alloys. The radial distribution function indicates that a tetrahedron is the dominant structure unit of the amorphous alloys, as expected from the dense random packing of hard or soil spheres. The stacking of tetrahedra is not sequential but the main coordination polyhedron is an icosahedron, because the average coordination number is 11-12.