Short- and medium-range structure characteristics of amorphous alloys

In the structure of amorphous alloys, the short-range order is rather close to that of the crystalline counterparts, while the long-range order is almost lost. The medium-range order does characterize the structure of amorphous alloys. The origin of the medium-range order has often been recognized as a connectivity between polyhedral structure units in amorphous alloys. The topological mechanism of crystal-to-amorphous solid state structure transition is demonstrated as a conversion of octahedral structure units into tetrahedral structure units. The medium-range chemical order has been observed in some cases of metal-metal amorphous alloys. The low-energy excitation (1-3 meV) currently found for metal-metalloid amorphous alloys, often called the Boson peak, is spatially extended to the medium-range length and very sensitive to the structure relaxation below glass transition temperature in amorphous alloys.