NEW STRUCTURAL MODEL FOR AMORPHOUS TRANSITION-METAL SILICIDES, BORIDES, PHOSPHIDES AND CARBIDES

A new model for the so-called transition metal-metalloid glasses has been constructed in which groups of atoms - coordination polyhedra with defined local geometry - are packed randomly to form a dense, three-dimensional array. Specifically, the coordination polyhedra are trigonal prisms containing six metallic atoms in a nearest neighbour sub-shell around a central non-metallic element with three further metal atoms at somewhat larger distances. They are essentially identical to the structural units observed in crystalline transition metal borides, carbides, silicides and phosphides. Computed density, neutron structure factor and radial distribution functions are in agreement with experimental data for a-Pd4Si. The local coordination can be distorted and changes in the properties of this structure provide some insight into the atomic rearrangements which take plave when metallic glasses are annealed to low temperature. Such stabilized" glasses appear to contain structural units which are more regular than those found in rapidly-quenched glasses. © 1979."