A new structural model for transition metal–metalloid glasses

CONCEPTUAL notions of the structure of metallic alloy glasses have generally developed from purely geometrical sphere-packing models proposed for liquid1 and glassy2,3 monoatomic metals. The assumption on which these models are based is that the glass consists of a random arrangement of spherical atoms of each element—the so-called dense-random-packed (DRP) model. Glassy ‘metallic’ alloys of two or more chemically dissimilar elements can also be represented in this way, local atomic arrangements arising by chance, constrained only by geometrical factors such as the ratios of atomic radii. Construction of the model described here is based on an alternative principle commonly observed in amorphous solids of other types, namely that local structure is well-defined and almost always identical to that found in crystalline forms of the material. The properties of such a ‘stereochemically designed’ model have been computed and are found to be in reasonable agreement with high resolution neutron scattering data for glassy palladium–silicon alloys.