STRUCTURAL MODELING OF TRANSITION-METAL-METALLOID GLASSES BY USE OF TIGHT-BINDING-BOND FORCES

A recently developed tight-binding-bond approach for the calculation of interatomic forces in disordered materials is extended to amorphous transition-metal-metalloid alloys. It is shown that the interaction of the transition-metal d electrons with the metalloid p electrons leads to strong covalent bonding forces that are reflected in a pronounced nonadditivity of the pair interactions. The structure of the amorphous alloys is modeled by a simulated molecular-dynamics quench. Results for Fe-B, Ni-B, Fe-P, and Ni-P glasses are in good agreement with diffraction experiments. It is shown that the covalent bonding forces lead to a chemical and topological order similar to that postulated in stereochemically defined models based on the packing of trigonal prismatic units. The molecular-dynamics simulations also predict a medium-range order (concentration fluctuations on a scale of 15-20 angstrom) in agreement with the existing small-angle scattering data.